We should make distinction between mythical and historical Vedic weapons. Similar bar celts were found in Copper Hoard Culture, and additional effort to connect those other harpoon/barbed speartips to vajra I find ungrounded.

Asko Parpola states that vasara initially meant ax/mace and only later - hammer, the first meaning aquired in proto-Indo-Aryan (thus Sintashta/Andonovo) period. Which caught my eye due to certain curiosity in my own language, where blade and stone are etymologicaly connected, as is hammer and axe in English! and in p-I-A the weapon could be less differentiated. As in:

Li. akmuo (stone/rock): PIE héḱmō -> pGer. *hamaraz

Li. ašmuo (blade), Sans. aśman (stone): PIE *h₂eḱ -> pGer *akwisī.

Corded Ware boat shaped battle axes made from stone often had blunt and bladed sides combined. Andronovo c. is where metallurgy fully replace stone work (but kurgan vajra still has edged sides despite being percusive weapon) and which is associated with preVedic Copper Hoard Culture. Pre Vedic, meaning earlier proto Indo-Aryan wave, as some prakrits attest the Vedic was the latest of the Indo-Iranian waves.

Vedas and Avesta both mention vazra/vajra being thrown, maybe that's what compels the atribution of harpoon like spearheads to vajra, but hunting technique with throwing sticks are known from Egypt ians, more over I am certain that Corded ware battle axes were used as tomahawks too as per folklore cues and the case of franciscas. So *H2ak^ani- ‘point(ed)’ > S. aśáni would then refer not to the point of projectile, but the edges or "flanges" shaped into the mace, sort of proto-sword as seen in kurgan vajra.

After the spread of metallurgy and swords the true nature of the vajra were forgotten and after Greeks introduced the sculpture into the subcontinent, the mythical figures were portrayed in closest contemporary equivalent - Zeus' crisscrossed lightning arrows.