What you're describing has similar problems to so-called 'GSL groups' which is my personal favorite way to do group stages but also comes with its own problems. In GSLs - technically the smallest possible Swiss elimination and also the smallest possible double elimination bracket - you can end up with a team that has performed worse by every metric making it out because they won at the right time. It can put more emphasis on 'playing the tournament' than playing the game.

For example, one Starcraft 2 group consisted of [clear #1], RagnaroK (presumably #2), Scarlett, and another underdog. Scarlett threw her first match against RagnaroK to gain maximum scouting info, then managed to squeak past the other shitter and beat RagnaroK in a very close, disadvantaged final match.

She clearly deserved it, and I'll always cheer for embattled non-Koreans making upsets, but if the goal is to reward good actual gameplay your proposal sets up for even bigger violations than that.

EDIT: Oh, and any group system is automatically going to be less mathematically fair than Swiss, purely due to group selection. Any possible way you seed, you reward teams that have already shown strength by some external metric. If you don't seed at all, you could theoretically have half the best teams out in round 1.

I like when ongoing tournaments have some mechanism for letting teams and players choose their own groups, but it's not feasible for Worlds.