Well, it's not going to matter because literally everyone already knows about this and chose to ignore it, but alright...
The game is time consuming as it is. Extremely so in comparison to the return. However, PvE for the most part doesn't require my active participation, so it's not overly bothersome. PvE progression is also something that can be done at whatever pace I want because it is static, and fusions aside, it's really not that big of a deal if I'm gone for a week.
Not so with PvP. Not only do I have to be there to pick the fights and play them out, but then there's the refreshing every 15 minutes which makes it inconvenient and disruptive in addition to being time consuming. If I ignore PvP for a week, I will drop in rank and lose out on GH medals, forge materials, tournament points, tier stat bonuses and so on. Tag team, for all the criticism it gets, is actually better in that regard, because it actually is optional unlike the classic arena, which is more like... "optional". Yes, I could ignore it. I could also only use 4* items instead of 6*. It'd hold me back approximately the same, yet I doubt anyone would seriously suggest that it's a viable long-term strategy to do that. Tag team, at least, is more like a nice bonus, but not a critical one. In both cases though, it forces me to play the game at a pace set by others, not by myself.
My GH is now fully upgraded and the loss limit in the classic arena allows me to maintain my rank without too much stress. Tag team is still tag team with all the horrible design choices it involves, but like I said, it's not something I feel particularly pressured into. I'm finally at a point where PvP doesn't really bother me, and it's entirely because I don't have to participate in it. Oh don't get me wrong, the classic arena is still utter trash, possibly the worst implementation of PvP I've ever seen in a game (though admittedly I don't have a lot of references), but just sitting in G5 is doable with minimal effort at least, so I don't want to rock the boat and inevitably make it worse.
Enter live PvP, which is everything I hate about the non-live PvP, but much much worse. Matchmaking will take time. The team pick/ban will take time. The matches themselves will take time. On top of it, I have to plan my life around the time when it's even available. All of that I could live with, if I didn't have to participate. But I do. There will be quests. There will be tournaments, quite possibly some required to complete fusions. There's a fresh new hell in GH 2.0, Gotta-Catch-em-All Edition. CvC points, tier bonuses, and who knows what else. And yeah, I could just not do it. Sure. I could also play the game with my feet. It's doable. Awfully inconvenient though.
So if you want a TLDR: the game is time consuming and stressful enough as it is. PvP is by far the worst offender in that regard. Adding more of it, in an implementation that promises to absolutely dwarf the previous ones in both regards, is really not the direction I want to see. Make it optional and I won't have a problem with it (what an interesting and fresh concept; adding a feature to a game just for fun), but right now it appears to be about as optional as running dungeons is.