I think a healthy mix of idealists and realists is necessary.. With senior developers representing a good majority of the former.
I think your company is suffering from bad architecture design more than anything else. It seems like everything is tightly coupled with little room for modifications. This probably means those senior developers weren't really senior to begin with. This tends to happen at startups where business is prioritized and people get hired with inflated titles. I have seen that happen in a lot of startups.
But you are right! The company is suffering from horrible architecture.. And any attempts to change it are near impossible because of the sheer amount of code and processes that we have. It seems like a never ending battle