It's more about the setup than being "too big"
Yes,a hamster may feel overwhelmed in something with little to no roof cover that is a square meter or larger,but if it is set up appropriately with deep substrate and lots of roof cover(and hiding places in general)it will be fine.That being said if a cage isn't set up right and has minimal roof cover a hamster is going to be nervous,being prey animals which absolutely need lots of roof cover.
Something else that can be done to help with nervousness along with the right setup is properly transitioning to a larger cage.This barely ever gets addressed,even though it is very important!Starting with a temporary divider in a larger cage then slowly allowing more space and doing a gradual expansion of the hamster's environment is much better than just jumping right to a larger cage.Not many people think about this along with setup,but it is absolutely crucial when it comes to changing cage size!
Another issue would be that people might assume their hamster should be automatically just as friendly as usual if they upgrade in cage size,which is a bit silly.It's just like any other cage change or bringing a new hamster home,they need to at least settle for a few days otherwise these issues can just get even worse.Not sure why this isn't thought of either,but it also is very important.