>> _Anecdotally, I've replaced OOP with plain data structures and functions._

I think this is why FP is becoming more popular these days but I'm not sure some people get why. The problem with OOP is you take a data set and spread it all over a 'system' of stateful (mutable) objects and wonder why it doesn't/can't all fit back into place when you need it to. OOP looks great on paper and I love the premise but...

With FP you take a data set and pass it through a pipeline of functions that give back the same dataset or you take a part of that data out, work on it and put it straight back. All your state lives in one place, mutable changes are performed at the edges, not internally somewhere in a mass of 'instances'.

I think micro services et al try to alleviate this by spreading the OO system's instances into silos but that just moves the problems elsewhere.

IME microservices solve engineering process problems (i.e. synchronization, enforcement of interface boundaries, build and test scale issues), not technical problems in the product.