Some players are on MinMax overdrive
Call it what you want. By RAW, it’s a DC 15 Dexterity saving throw to avoid damage regardless of the size of the falling creature (beyond that if it’s tiny it does no damage at all). And that’s assuming you’re playing with the optional rules for creatures falling on other creatures causing damage.
I’ve seen that rule before. They didn’t carry it forward into the new rules, and for good reasons.
That rule comes from Tasha’s Cauldron of Everything which is compatible with the 2024 update so it’s still a valid RAW interpretation according to WOTC.
They carried forward all the other optional rules from Tasha’s, and not the that one. Clearly they didn’t like something about it.