Yes . Vajra is the strongest weapon and higher than Trinity weapons in terms of showings in ithihasas when it's powered by Vishnu and It's not even close. It killed the strongest demon in the universe .
Vritra is easily the strongest demon in ithihasas like Mahabharata and Ramayana. He prevaded the entire universe and was about to devour the three worlds and the gods .
Udyoga Parva Udyoga Parva 5.10
- सर्वं व्याप्तमिदं देवा वृत्रेण जगदव्ययम् ।
- न ह्यस्य सदृशं किञ्चित्प्रतिघाताय यद्भवेत् ॥
- समर्थो ह्यभवं पूर्वमसमर्थोऽस्मि साम्प्रतम् ।
- कथं कुर्यां नु भद्रं वो दुष्प्रधर्षः स मे मतः ॥
- तेजस्वी च महात्मा च युद्धे चामितविक्रमः ।
- ग्रसेत्त्रिभुवनं सर्वं सदेवासुरमानुषम् ॥
- “O gods, the entire imperishable universe has been pervaded by Vṛtra. There is nothing comparable to him that could oppose him.
- Formerly I was capable [of opposing him], but now I am incapable. How can I do what is beneficial for you? I regard him as exceedingly difficult to assail.
- He is mighty and exalted, and possesses immeasurable prowess in battle; he could swallow the entire three worlds, together with gods, Asuras and men.”
Indra himself mentions this again.
त्वं प्रभुः सर्वलोकानां त्वया सर्वमिदं ततम् ।
- त्वं हि देवो महादेवः सर्वलोकनमस्कृतः ॥
- गतिर्भव त्वं देवानां सेन्द्राणाममरोत्तम ।
- जगद्व्याप्तमिदं सर्वं वृत्रेणासुरसूदन ॥
- “The entire universe has been pervaded by Vṛtra, O slayer of Asuras(Vishnu) .”
Except Indra , all the gods were utterly defeated and were terrified of vritrasur . Vishnu entered the vajra and helped Indra in killing vritrasur.
- अदृश्यश्च प्रवेक्ष्यामि वज्रमस्यायुधोत्तमम् ।
- “Remaining invisible, I shall enter his thunderbolt, that supreme weapon.”
Similarly, When hiranyakashipu asked the boons from Brahma to become the universe and all the gods. Only a powerful god who is capable of defeating him with one blow is capable of killing him .
- The one who is capable of killing me, along with my servants, army and vehicles with a single strike of hand, may become my death.
That's make Vajra the strongest weapons in terms of showings .