That was my point. The game is balanced for party of 4 ONLY because it isn't using proper stats and rules. It's all based on homebrew and gimmicks.
But the COULD make it based on actual D&D 5e and party of 6 and the encounters would not really need to be changed. Then people would actually get a 5e experience. That's my point.
So, players who want party of 4? Change nothing. Everything as is.
Players who want D&D 5e as it should be? Bump party size to allow custom 4 characters with the ability to have total party size 6.
Then 3 homebrew nerfed imps are fine for party of 4, and 3 actual D&D 5e imps are fine for 4 customs and Lae'zel.
3 homebrew intellect devourers are fine for party of 4, but 3 actual intellect devourers with 5e stats and rules would be doable with party of 4 customs and Shadowheart.
Homebrew spider Matriarch lair is tough for party of 4, but still doable with actual 5e phase spiders and party of 6.
My point is that some think they'd have to redo encounters altogether to make party of 6 work. They'd have to add more monsters and jazz. Nope. Just do actual D&D rules and stats. Then party of 6 would be challenging and just what many of us are looking for.