We just can’t easily access it (hopefully “yet”).
4 4s are boosted at a time (5 if a required character in PvE or PvP), on top of being Championable. This puts them into the 5 level quite easily.
Now we just need to be able to get at them O.o
I don’t mean this as a cover or iso8 complaint (although both of these issues are currently elephants in the room). I mean this as an optimistic point. Once the Devs get around to a 4* shake up like the 3* shake up the game should look a lot better.
Keep Calm and Carry On!