Nope and I never really did. I found it more frustrating than anything. It reminded me of games like COD,BF, Destiny and so on, where the higher level players have access to better stuff. So it's a mode of the more you play, the better stuff your likely to have. Honestly, when I played Warzone it didn't even feel like Halo, it should be its own separate game. The only Warzone I play now is firefight.
Couldn't have said it better myself. I can't stand Warzone for its "rich get richer" aspect, which is built into the req system. Even without things the OP mentioned like full teams or JIP, I dislike Warzone because of its core mechanics.
I played Warzone a few times in the beginning, and I mostly hated it. I remember being frustrating with only having an assault rifle and Magnum, when everybody else had battle rifles. So no, I don't still find Warzone fun, if I ever did, and I haven't for a very long time. It's hardly a replacement for the BTB Heavies that I know and love.
I also agree with your points about Warzone Firefight, which is all I play in Halo 5 anymore. It would have been nice if 343 gave it more attention. At the very least they should have separate weapon and vehicle balancing for PvE, or just make the req stations refill all weapon ammo, because Warzone Firefight generally suffers from the way reqs are balanced for PvP Warzone. I don't think that would be a problem if 343 had prioritized it from the beginning, instead of cobbling it together later as an offshoot of the pre-existing Warzone.