Grenades need to be limited in halo because getting grenade spammed just ruins multiplayer, especially in Halo 2 where you can have up to 8 grenades and everybody is just grenade happy. For Halo2 please limit the grenades to at least two grenades and for the rest of the Halos even Halo 5, limit the count to one grenade. Please consider this grenade spamming might just make me stop playing halo altogether.
Grenades are limited in newer Halos and exactly for the reasons you listed. Try Halo 4 sometime. Contrary to popular opinion, it doesn't suck.
I disagree with limiting the grenades in Halo 2, if you're playing SMG starts and the other team all have BRs and controlling power weapons, you're screwed if you don't have a wad of grenades to use.

If you jump around and stay away from areas where you can get spammed a lot, you can avoid them more easily.