Yes, many drivers would have more than his 8 wins with that team. You say that not many wins are possible with Mercedes dominance, ok, I'll give you that. So you don't think that Red Bull have given him a car that can compete for pole positions? He has a meager 2 from 82 starts.
Nico Rosberg in the 39 races of the 2012 and 2013 seasons was able to get 3 wins and 4 poles.
You could say that Red Bull and Ferrari were too dominant in those years, so another measure to gauge driver performance could be fastest lap in the race. Mercedes bagged 6 out of those 39 FLs (Rosberg with four, Lewis and Schumacher with one each), that's a 0.153 success rate; in the 82 races that Max has raced for RBR, the team has achieved 16 FLs for a .195 avg. That's 7 FLs for him, 8 for Danny Ric and 1 for Gasly.
Point being? Above average driver in a fast car. Lucky to be driving for a team that was able to salvage a podium with 20 seconds to spare.