PvP: I don't really do PvP. But I can see how this change might be too harsh in relation to PvP. I understand people who argue that this is a bad change for PvP if people can just kill their pet and cripple them extremely. They should probably do a PvP talent which reduces the cast time.
Raids: For raids it doesn't really make much difference. The pet doesn't really die anyway :P
M+: For M+ I think it's an okay change. The fact that we get a little punishment when we pet tank etc. is fair in my opinion. Currently the pet tanking is pretty OP in M+.
Solo Content: For solo content I also think it's an okay change. It's fine to have a small punishment for people who forget to heal their pets in solo content. Horrific Visions for example is currently extremely easy as a Hunter because your pet handles the most of the damage taken. So I think it's fine to have a small punishment if we pull too big or forget to heal our pets.