This seems true at first, but after having worked with C# a while I'm not so sure about that. OO introduces some weird issues that aren't immediately apparent: 1. Verbosity When the shortest method call looks like "abcObject.functionXYZ()", code gets huge really fast character-wise. This actually does make it harder to read and debug existing code.
2. Multithreading Multithreading in any programming paradigm is a pain, I'd give you that. But OO exacerbates the problem because of the way each property of an object is essentially a global state within its local scope. It makes it quite tricky to enforce thread safety.
Having said that, I'm not sure that rewriting it in, say, a functional style would make things simpler. Sure it is easier to prove correctness, but as soon as you introduce IOs, everything goes to hell. I guess OO seems to be the worst pattern, except for all others that have been tried.