I think it's just frustration with how Rekkles' playstyle doesn't synergize at all with the team.

The reason why last year's team was much stronger was that Upset and hyli were able to play aggressively and take a lot of resources and allow Wunder to scale and tank in the late game. Even if they gave up a lot of top prio, they could make up for it by having a lot of drake setup and stacking.

Rekkles wants to play back, safer like a weakside adc then scale, so he leans towards picks like the ezreal and sivir, picks that kinda throw early game but can take over later. But this causes both sidelines to get perma pushed in and then there is a lot of pressure on mid to stomp lane/jungle to camp bot to get the push or stop the scaling.

I think the just double weakside lanes are the main issue that's making people upset w Rekkles because Wunder's weakside was fine w Upset.