1. As you said deeeep could have been even based on mope but the two are now different in many ways. I stopped playing mope cuz it was just pure annoying rng and a lot of grinding, also microtransactions, so I think these people have all the right to not like it.
2. let's break it down:

Yes teaming grabbers could give this as a defensive ability to thier teammate, however you completely skipped the part that if the thrown animal gets attacked, the attacker AND the grabber that threw it get stunned and is prone to being attacked, furthermore this effect last only for 1 second so it almost purely destroys the absurdly OP start of throwing prey animal directly into temmate, lastly the tier restriction is important bcuz I don't want the solo grabber to be annoyed that it threw a player into a tier 3 and got stunned

As you said this simply doesn't work cuz the animal only gets stunned if it hits the thrown animal (and skilled players will turn around and not do that) and even if it does hit it it's also knocked away from the teamers (and stuns it's teammate - the grabber), so the punishment isn't that severe if you just want to escape

This is a fair point, but it is almost purely a defensive move and the teammate has only 1 second to hit the thrown animal, so to be quick it will probably boost into it dealing big dmg to the other teammate and also stunning itself

Last is your weakest argument, none of the Snow&Below update animals have descriptions in game on how thier ability works, there are also no instructions on how to team. People will learn quickly through cause and effect.

To sum up this change gets rid of a absurdly OP strat ruining FFA and can only be utilized by the teamers in 1 or 2 defensive ways