3.5 was edition I played the most. It was a reason why I quit RPGs for nearly a decade because I hated it so much.
Every time I see another meme about how amazing 3.5 Tarrasque is, I remmember how amogn actual 3.5 players Tarrasque was the biggest joke. It was always brought up as definite proof designers have no idea how to make good monster. It was laughably easy to beat. A wizard could casually solo it, the same abilities people now miss in 3.5 amounted to ribbons. It was a laughingstock, forums had 100+ pages discussions how to fix it and general consensus was it’;s beyond saving. It was first proof in 3.5 if you cannot use magic you’re only good to roll over and die.
I honestly don’t know if everyone claiming 3.5 Tarrasque is such a horrifying monster are trying to rewrite history or unintentionally proving what a broken, unplayable pile of garbage 3.5 was, if it’s biggest punching bag is actually dangerous in a different, better designed game.
I mean, I think the generic DM response to that is going to boil down to “The owls won’t behave that way”. Its for the same reason DMs blanche at the “Summon a whale 40 ft off the ground” technique (and why rulebooks started adding conditions about where and how things could be summoned, period).
The magic bag full of boulders is a classic munchkin weapon, but it does require some degree of preparation and isn’t the same level of mechanically out-of-the-box function as kamikaze owls. Even then, a general DM adjudication to these kinds of techniques would be to limit the damage to an equivalent spell effect. So a 3rd level Shrink Item will let you do (level)d6 damage from a hurled boulder. And you can only practically fling one of these a round.
That allows people to be creative to a degree (dropping a boulder down a mountainside will have different consequences than lobbing a fireball, and everyone can lean into that) without exploiting the mathematical discrepancies of fall damage versus every other kind of damage.