You can never trust clients to behave. If your goal is to reduce infra cost, sure, rate limiting is an acceptable answer. But is it really that hard to throw on a cache and provision your service to be horizontally scalable?
Scaling matters, but why pay for abusive clients or bots? Adding a cache is easy; the hard part is invalidation, sync, and thundering herd. Use it if the product needs it, not as a band-aid.
