But if someone has “hit their limits” like the article claims it means they can’t go on anymore.

When somebody "hits their limit" that means they are stagnating and not falling or collapsing. It is also important to be clear that this is about the economy.

If the Russian war economy would not be able to increase overall production(not necessarily production of specific weapons, but overall), you would expect them to slow down their advance and take higher losses, as the soldiers lack weapons and whatever to make that happen. We also we see fewer air attacks against Ukraine.

That seems to be the case. Russian personal casulties are generally pretty high and they are not taking a lot of land. At the same time Shahed attacks are 30% down in June compared to May.

Big losses would happen, if Russias economy collapses and only some time after that. That might be the case given the current fuel situation in the country.