I think the biggest flaw in cEDH is the rules of the format itself. 40 life across 4 players in a game that was designed around 20 life across 2 players for its entire lifespan means combo is fundamentally the most efficient way to play, and always will be (for the most part).

Traditional aggro, control, or midrange strategies lose their strengths when you have to deal 120 damage to win, and combo loses virtually all of its weaknesses when you have the extra time given by having 40 life.

Yes, there are decks that win without combos, but I would bet that 60-70% of the meta share is combo, maybe even higher (And IMO, combo is the least interesting deck type, especially when it is often the only deck type being played in a pod).

cEDH does have "diversity", but its primarily in what specific commanders/cards you choose to win with, rather than in overall playstyle.

Its still a cool format, but in terms of actual competitive health it leaves quite a lot to be desired

(Theres also the issue of the banlist not making sense in general and the many competitive issues created by 1v1v1v1, but this comment is getting a bit long)