Don't get me wrong, PvP has his casual side as well and it's perfectly fine. I may have used a poor choice of word, but what I meant is that PvP should be able to drag more people byt itself, not just by being another PotD. New players that will eventually come there for a first time by curiosity before everything else. But showing them a Frontline were people just "guard base", or a 8v8 where half of the team is throwing match. They'll just end up not going there anymore once they'll reach 70.
I think lots of people only see rewards as the only effective way to drag players in this mode, it's true it has a role in this, but that's not the only reason. Leaving aside Garo event and right now the exp gain, there were 2 moments in 3.x series where people started playing a lot frontlines again; 1st it was between 3.0 and 3.1, pops were not so bad despite having the stupid GC restriction, ofc, not much during night (ppl still need to sleep). 2nd was when shatter went out. I think most people wanted at least to give it a try by curiosity. And basically, none of those moments brought any new reward but tomestones ( that was already a thing during ARR, correct me if I'm wrong please)
So ofc, both of them were followed by down time, mostly because PvE got new content that changed people priorities. But IMO, the fact that at that time we still had GC restriction could have stopped some people to keep playing pvp casually. It was kinda a snowball effect: ppl stop queueing because they are doing new PvE content >>matchmaking goes slower >> less pop >> people find wait too long >>Shittier matchmaking >> less pops etc...
What I'm trying to say is that rewards aren't the only thing that brings people to pvp. However, the stupid GC restriction was the main cause that let those modes die.
Devs got it at 3.5, Garo event has been possible because they removed GC restriction. Otherwise, it would have never worked. Put it back now and no one will go in frontlines for xp, no matter how good it is.
[EDIT] However, I stay on my position concerning 4v4 ranked. This the only competitive mode in pvp, people don't go there to get XP, tomes or training (except during pre season ofc). More over, since it's out, matchmaking got worse and worse at the point that having the rank gold in season 3/4 means nothing regarding players skills (30% winrates needed). So yeah, the only people that go there are those that want to try to climb the rank, if that's not the case, just don't.
[EDIT 2]
This is probably the best idea that dev should look into seriously if they want to keep exp as a reward that, while punishing afkers, reward those who actively participate in the match; They should also add the same bonus that is going for tomes: if you lose, next time you win, your xp is increased by x %. That is encouraging for any player that is giving his best.