Well, WQ rewards are really disruptive for the PuG raiding and M+ scene. With "normal" rewards capping at 372, and elite quests giving 382 and weekly 380s-390s as vault substitutes. Then you have elemental storms and super rares also scaling into the 380s, plus the 4 up to 405 crafts, with additional crafts in the 380s available. If you add world even queued content (LFR and timewalking) you also access more gear, but LFR can largely be skipped already. Tier gear can be acquired via catalyst + primal storms / world boss, but this took too long to unlock.
When I look at M+ groups in the group finder, they are about 80% 15+, with around 20-30% being 20+. As someone who is just starting out doing M+ this expansion, there is a very limited pool of "learning" groups at lower keys. I can of course run my own groups, but the point is that current WQ rewards already disrupt the lower brackets of PuG group content, since most people will take the path of least resistance to the level of play they enjoy, then play that. Most people do not enjoy Sub 10 M+ keys, so they will just do world content for rewards up to M+ 10 level, and then start doing M+, since it is quicker anyways.
As a primarily solo (+ queued group) content player, I do sympathise with wanting to keep building your character, and I think it would be nice if they added an upgrade currency from primal storms to upgrade this gear (which would naturally be slower than M+ since the gear from primal storms always start at 385, but mythic+ item can start at a higher level). However, I think just raising WQ iLvL rewards in the current game environment will make M+ and Raiding even more inaccessible since no one will be PuGing the lower difficulties.