20 years experience with OO code. Over time, OO always leads to entanglement due to inheritance based solutions that seemed like a good idea at the time. Eventually, these become the basis for many other parts of the system.

You combine the potential for side effects in the code with a tree that can't easily be changed because of how many other things it will negatively affect and you end up with a code base that is harder and harder to change the larger it gets.

In a FP approach, this is a class of problems that you can't easily replicate. Yes there's a learning curve to operating in a FP style, but once you're able to move quickly with it the long term rewards are a byproduct.

The OO solution to avoiding this problem is to build with microservices instead, which forces different parts of the system to be isolated and minimizes the negative effects from entanglement...but microservices come with their own maintenance and speed of development headaches as well.