The-Magic-Sword
Small Ball Archmage
After a lot of tinkering with 5e, multiple campaigns worth of play, back to basics tests, discussions with my players, an attempt at a power neutral magic item system, banned feats, a small career as a homebrewer on unearthedaracana, an attempt at the rules in the back of XGTE, I am proud to report we finally fixed it (by switching to pf2e)I've run games up to 20th and never had an issue. It could have been clearer but the rules for encounters in the DMG seem to be based on 4 PCs, no magic, no feats, novice players.
Not sure what you mean by "magic item pain point" but advice (some actually worthwhile) is a forum post away.
Edit: to clarify, i imagine the difference is that i play with players who push character optimization pretty far, fairly consistently.