But of course it has to do with blocksize.
Blocksize is a check on economies of scale so as to level the playing ground. It is absolutely necessary while Bitcoin is still relatively small. Without it the entities with the most resources will make use of the technology available to run out of the market any smaller players.
that is only true if the entity with the most resources has more than 51%.
otherwise i expect smaller players to team up in such cases and ignore blocks as soon as a big player start to behave badly.
it is in their best interest to do that.
we can see this with: most home miners go to the biggest pool like flies going to the brightest light. but - until now - whenever a pool got to much hashing power the community realized that it is bad and hashing power got more distributed again.
You don't seem to grasp the impact of this. In this outcome there is no "smaller players".
There is an unlimited amount of capital which can and WILL be leveraged to install hashing facilities that can and will accept big blocks. The competition in that scenario is not between large miners and smaller ones, it's between large miners only.
What you get is a handful of giant corporations running mega mining operations coupled with node datacenters that essentially make smaller players irrelevant.
Home mining is destined to be a thing of the past. Even the most dedicated hobbyist will be run out of the game. You can't imagine a situation where they will stay relevant and therefore by looking for their own best interest will put a check on large scale operations. That's just not how it works.