Then what would be the advantage of finishing top of the first group?
What you could do is have the top 4 teams from each group advance to the next phase in which there would be another two groups but this time have 4 teams in each group. The top two teams of the first phase would switch groups. That offers some kind of advantage to the top two teams because they'd have to play the weakest two from the other group, where as the weakest would still have to play the best two from the other league.
you dont have any advantage to finish top of first group, u need to finish among top 3, think about it, your idea sounds okey but only in situation where we have more or less 8 equally strong squads, but we have 2 top squads, then tp, then a few mid tier ones and low tier ones. There will be no real motivation anyways in the first group stage, how hard would it be for Exalt or Blood to become among top 2 in group of any random other squads put together. It doenst make any sense.
Your system would infact increase the number of pointless squads and would create a situation where 2 top squads might not even face each other during entire season.
Just a quick comparison. IN your system blood and mut win 1 group and exalt tp other, they now face low tiers from other division. in playoffs blood would meet tp and mut exalt, while tp and mut have even no games between each other to determine which is better.
IN my system all top 6 squads would have to play each other at least once, best 4 will be found out and playoffs commense.
Also i think it might be even a good idea for top tier squads to have a few games vs mid-tier without the purpose to win the first group. It will give chances to benchers to play and make the league more entertaining for all participants, Also as top tiers dont need to win all games as fast as possible, it will also give low and mid tiers more chancces of pulling surprises vs top squads if they use benchers.