From expert games come characters/roles with a bunch of stats (a much smaller bunch than in regular expert games). But the roles are ready-made, like in mafia.
From mafia come the NK roles (but many NK roles, not just 1-2) and the game's goal: kill everyone and win.
The fundamental difference is the absence of a team that clearly outnumbers the others (i.e., a town). That is, the ALLIANCE is a more important part of the game than calculating the "organized minority" (i.e., the mafia) and lynching them all.
It's unclear why this format "didn't click" with you, but the issue here clearly isn't the complexity of the sets... It's something else.
P.S. The HeroesWorld mafia format on that forum also didn't appeal to them. But the reason there was specifically the rejection of HeroesWorld rules, and it's simply impossible to play the format used here under their rules.
Если где-то чего-то убудет, то в другом месте добавится.
(Закон сохранения).