I think that even the unarmoured elephants are a little to weak- IIRC they don't have any armour at all right? That would mean that a 4hp elephant gets killed by 4 well placed arrows. Elephants have pretty thick skin - sensitive though, wich is why elephants would panick after being showered with projectiles - that would protect them from serious injury from arrows. Javelins would be better.

It's worth remembering though, that the Seleucids only used their elephants as an anti-cavalry screen at their flanks. The prevalence of skirmishers in the east probably would have had something to do with this.