Ravana was the strongest rakshasa of Treta yug because of the boon he recieved from Brahma.
Ravana had a boon from Brahma that no god or demon can defeat him in fight
Ravana replied, ‘May I never suffer defeat at the hands of gandharvas, gods, asuras, yakshas, rakshasas, serpents, kinnaras and demons.’
Indra , Vayu and Yama fled away from his mere presence .
Scared of being oppressed, they assumed the forms of other species. Indra turned into a peacock, Dharmaraja into a crow, the lord of treasures into a lizard and Varuna into a swan. Ravana, the lord of the rakshasas, approached the king and said, “Give me a fight or say that you have been vanquished by me.”
Ravana overpowered Indra in archery and broke his bow
Shakra stretched his large bow, which emitted an extremely large sound. The sound of it being twanged resounded in the ten directions. Indra stretched that great bow and brought down arrows that were as radiant as the sun on Ravana’s head. However, the mighty-armed Dashagriva remained there. He showered down arrows and dislodged Shakra’s bow. They fought against each other and showered down arrows in every direction. Nothing could be discerned then. Everything was covered in darkness.’
most people quote Sage Agastya,’s statement of Meghnad being powerful than Ravana and Kumbhkarana. but statements can never be taken literally.
If Meghnad was more powerful than Ravana then why did Vishnu take birth as Lord Rama to kill Ravana.
And the very point of Sri Rama’s birth was to kill Ravana and not his son. Sri Vishnu and Devas did not even care for the elimination of Indrajit or Kumbhkarana. Their aim was to kill Ravana only.
तत्र त्वं मानुषो भूत्वा प्रवृद्धं लोककण्टकम् || १-१५-२१
अवध्यं दैवतैर्विष्णो समरे जहि रावणम् |
"Oh! Vishnu, on your taking birth as human through the wives of Dasharatha you eliminate Ravana in war, who has become exacerbating and thorny to all worlds, and who is otherwise not eliminable for gods. [1-15-21b, 22a]
- Valmiki Ramayana, Bala Khanda.
this alone proves how powerful Ravana was. Vishnu himself had to incarnate as Rama to kill him and Lord Rama was the strongest warrior of Ramayana.
Ravana was powerful enough to lift the three worlds. A feat that Adikavi Valmiki himself mentions.
हिमवान् मन्दरो मेरुस्त्रैलोक्यम् वा सहामरैः |
शक्यम् भुजाभ्यामुद्दर्तुम् न शक्यो भरतानुजः || ६-५९-१११
Though he was able to lift up Himavat, Mandara and Meru mountains as also the Three Worlds with the Gods, he could not raise Lakshmana the younger brother of Bharata.
- Valmiki Ramayana, Yuddha Khanda, Sarga 59.
Apart from this Ravana lifted the Kailasha mountain along with Lord Shiva and Parvati as per Uttar Kand.
Ravana had all the missiles and Valmiki Ji himself mentions it in Aranya Khanda.
सर्व दिव्य अस्त्र योक्तारम् यज्ञ विघ्न करम् सदा |
पुरीम् भोगवतीम् गत्वा पराजित्य च वासुकिम् || ३-३२-१३
तक्षकस्य प्रियाम् भार्याम् पराजित्य जहार यः |
He who is a marksman of every divine missile, and an ever interdictor of Vedic-rituals, and who on going to the city named Bhogavati, the capital of Naga-s, and on defeating Vasuki, the King of Serpents, has abducted the dear wife of Taksha on molesting her, and Shuurpanakha saw such a molester of others wives. [3-32-13, 14a]
- Valmiki Ramayana, Aranya Khanda, Sarga 32.
Ravana,’s Brahma armour was able to tank the Sudharsana chakra of Vishnu and Vajrastra of Indra dev
He also observed the two outstretched arms of the gigantic lord of ogres, which were adorned with armlets of gold and resembled a pair of flags raised in honour of Indra which bore scars of wounds sustained in combat with the ends of the tusks of Airåvata, the carrier of Indra, nay, whose fleshy shoulders had been lacerated by the thunderbolt of Indra and which had been injured by the discus of Lord Visnu; which were fleshy and culminated in uniform and well-formed shoulders, were tough-jointed and powerful, bore auspicious marks on their nails and thumbs and were characterized by shapely fingers and palms.
~Sundara Kanda , 10
He defeated the entite army of vanaras using Tamastra
Ravana overpowered Hanuman in wrestling fight and defeated Lakshmana twice using infalliable weapons in fight.
Ravana had defeated almost every warrior from Rama,’ s army except Lord Rama and Hanuman
Ravana equipped with his Brahma armour fought with Lord Rama for seven days non stop.
At one point of time, Rama was said to be eclipsed by Ravana’s valor and momentarily was so overwhelmed that he couldn't even fit the arrows to his bow.
He tore the standard of Indra’s chariot with a single arrow aimed at it, and having felled the golden ensign from the top of the chariot down to the seat of the chariot,
Råvana struck Indra’s horses as well with a series of arrows. Seeing Råma afflicted, the gods, Gandharvas (celestial musicians) and Cåranas (celestial bards) alongwith the devils as also the Siddhas (a class of demigods endowed with mystic powers by virtue of their very birth) and the foremost Rishis became despondent; while monkey chiefs alongwith Vibhishana felt troubled.
Seeing the moon in the shape of Råma eclipsed by the planet Råhu in the shape of Råvana, the planet Mercury stood assailing the constellation Rohini presided over by the god Prajåpati (the lord of creation), the beloved of the moon, spelling disaster to all created beings. Burning as it were in fury, the ocean rose high at that time as though it was going to touch the sun, its mist-wreathed waves turning round.
Looking ashy in colour and assuming a stern aspect, its rays grown faint, the sun appeared with a headless trunk in its lap and united with a comet. The planet Mars too evidently stood assailing in the heavens the constellation Visåkhå, presided over by the gods, Indra and Agni (the god of fire), which is propitious to the kings of Kosala. A bow held tightly in his hands, Råvana, the ten-headed monster, with his ten faces and twenty arms looked like the Mainåka mountain.
Being overwhelmed by the ten-headed ogre, Råma for his part could not even set his arrows to his bow in the forefront of the battle. Knitting his brows, his eyes turned slightly crimson, he gave way to a fierce rage as though he would consume the ogres. Casting their eyes at the countenance of the sagacious Råma, who was provoked to anger, all created beings were seized with terror and the earth began to quake.
Ravan was also shown to compete with Lord Rama himself in archery without the aid of Brahma armour
Seeing him deploying increasing efforts in the struggle, Kakutstha, as if smiling, took up his sharp arrows and loosed them in hundreds and thousands. Observing them fall, Ravana, with his shafts, covered the entire sky and, on account of that rain of dazzling missiles loosed by those two antagonists, it seemed as if a second heaven of weapons had been created and, amongst them, there was not one that did not attain its target, not one, that did not pierce another and not one, that was loosed in vain; and, having collided with one another, they fell to the ground.
Thus Rama and Ravana fought with an increasing supply of weapons and, in the struggle, they showered down their spears without pause to right and left, so that these formidable weapons covered the firmament; Rama striking Ravana’s steeds and Ravana striking those belonging to Rama; thus, both exchanged blow for blow and both, in the height of anger, entered upon a tremendous duel causing the hair to stand on end. Then with sharpened arrows Rama and Ravana continued their combat and, contemplating his broken standard, Ravana was consumed with rage.
Ravana (with his Brahma armour) was the strongest warrior from Ramayana after Lord Rama.
even after his death he was praised by Lord Rama for his bravery
अधर्मानृतसन्युक्तः काममेष निशाचरः || ६-१११-१००
तेजस्वी बलवाञ्शूरः सङ्ग्रामेषु च नित्यशः |
"This demon may be full of unrighteousness and falsehood. But, he was brilliant, strong and ever a brave warrior in battles."
- Valmiki Ramayana, Yuddha Khanda, Sarga 111.