Yes, Hanumanji had the full capacity to single-handedly punish and even kill Ravana. It is evident from the Yuddha Kanda incident when Ravana and Hanumanji confront each other. Ravana punched Hanumanji on His chest, but since He is none other than Vayu Himself (as stated in the Valmiki Ramayana itself), it was like hitting the air itself, which resulted in no harm to the hair and a wasted effort.
But when Hanumanji mildly punched Ravana on his chest, Ravana vomited blood from 10 of his heads and fell unconscious. For a moment, devatas thought Ravana was dead. Ravana woke up and praised Hanumanji’s power. Hanumanji said, “You are praising me? This was just a sample of my real power. The real power is remaining!” Ravana ran away from there. That’s where Ravana stands in front of Hanumanji.
But the thing is, these vaanaras are not just mere Vaanaras. These are devatas. In the Valmiki Ramayana, Lord Brahma instructs the devatas to incarnate on the earth for Bhagavan Vishnu’s seva and NOT for helping Bhagavan Vishnu. So, as per Brahma’s instructions, Mukhyaprana Vayudeva incarnated as Hanumanji, Surya incarnated as Sugriva, Indra as Vaali, and Yama Dharma had already been born as Jambavan from Lord Brahma. Vishvakarma incarnated as Nala, and Agnideva incarnated as Neela. So, all these Vaanaras were devatas who had incarnated to serve Lord Rama in killing Ravana. As per the Valmiki Ramayana, they are known as the sons of Vayu, Surya, Agni, and all, but they are also the incarnations of that particular devata.
Lord Rama doesn’t need anyone to kill Ravana. Just by His mere will, He could have killed Ravana, but the thing is, these devatas who incarnated to serve Rama should get the chance to serve Him in killing Ravana. So, to give that chance to serve Lord Rama, Hanumanji and Lord Rama chose to take the whole vaanara sena to Lanka. If you are worried about so many vaanaras being killed in the battle, then don’t worry. Lord Rama, after killing Ravana, instructed Yama Dharma to return the dead vaanaras from the Yamaloka. Yama Dharma, following the instructions of Lord Rama, returned the dead vaanaras alive to Rama.
As per the Mahabharata Tatparya Nirnaya, Hanumanji Himself says to Ravana:
न रामबाणधारणे क्षमा सुरेश्वरा अपि ।
विरिञ्चि शर्वपूर्वकाः किमु त्वमल्पसारकः ॥
Which means, “Even the rulers of the gods, including Brahma and Shiva, are not capable of withstanding the arrow of Rama. What then to say of you, who possess so little strength?”
[SriMahabharata Tatparya Nirnaya, Chapter 7: SriHanumat Pratiyaanam]
So, Rama doesn’t need anybody’s help to kill Ravana. Hanumanji, with the grace of Rama, has the inherent strength itself. So, they both don’t need anybody’s help to kill Raavana. These Vaanaras are just to serve Bhagavan SriRama in this Ramavatara. Hanumanji could effortlessly kill Ravana as He Himself says in the Valmiki Ramayana, ‘Even if there are 1000s of Ravanas like you, then also they are nothing in front of me.’ Hanumanji didn’t kill him because He knew that it was Rama’s sankalpa to kill Ravana and only Rama must kill Ravana and nobody else.
If this is the case of Ravana in front of Hanumanji, then what is he in front of SriRamachandra Himself??
Hope this helps!
Jay SriRam!
SriHanumad Antargata SriSitaRamachandra Abhinna SriKrishnarpanamastu!