So as a player pretty deep into 5* land, I'm realizing what I miss most about this game is the variety in play. We all know the metas and the focus has been on adding characters to help shift things. I think your focus, while well meaning, is in the wrong place.
I'm not sure if it's been mentioned but what we need is character restrictive events in PVP. Since I've been playing (for like 8 years now), PvP has been focused on highlighting a specific character and the weekly boosted characters. The season themes have been on the Infinity stones since Infinity War dropped in theaters. It's time to move on.
The closest we get to what I'm thinking about are the 'Class of' PvP anniversary events. We need more of that! These characters have so many classes/tags that are only being used in skills and PvE but not really relevant in PvP.
We have a Civil War PvE but not a PvP. Think about the combinations and varied character use when you can ONLY use Avengers in that PvP. What if there is a Mutant only PvP? (I'm biased and would really love that!)
This thinking doesn't have to apply to just events but entire seasons. New season themes where the events match and demand diverse, thematic character use.
I feel like this is what the game needs to feel fresh again. The current rotation is very mundane to me and I find myself skipping a lot of events out of boredom. I have a lot of characters and would really like to use all of them, but I need a reason. But as things are I can only use what's boosted or meta/counter-meta.
Food for thought.