So the solution seems painstakingly obvious to me.
Put an iLvL cap on each PvP bracket and never allow the iLvL range to exceed 20 points.
e.g. Level 40-49 PvP bracket has an iLvL range of 40-60. Blizz could come in and put an iLvL CAP of 50 for that specific bracket; problem solved, even for premade groups.
This is especially possible now that they have implemented the level squish (& less brackets too).
If they do this, then they could also let XP-OFF characters queue with normies again.
P.S. I still don’t know why Legion went 100% communism with their iLvL restrictions in PvP. In legion, if I recall correctly, every 10 item levels equated to +1% all stats. I always thought it should be at least 2.5% all stats.