You raise an interesting point about the historical use of elephants in warfare. It's true that elephants were primarily used to break enemy lines and cause chaos, rather than as siege weapons to breach fortifications. Their ability to trample over infantry and disrupt formations made them incredibly valuable in certain battle scenarios, especially in open-field combat where the threat of a rampaging elephant could cause a rout.
However, as you mentioned, they were expensive and unpredictable, which made them a risky option. The key to using them effectively was the timing and placement within the army, and, of course, the ability to counter them. Light infantry with ranged weapons, or even cavalry, would be effective counters, as they could harass and kill elephants before they became too much of a threat.
In terms of game mechanics, I think the representation of elephants as powerful heavy infantry killers makes sense from a gameplay standpoint. They would need counters like ranged or light infantry to balance their power and avoid them from being overpowered.