I disagree. There are incompatible design disciplines and architectures. 100% functional code is a lot better than 99% functional. 99% functional is a mess. 10

I disagree. There are incompatible design disciplines and architectures. 100% functional code is a lot better than 99% functional. 99% functional is a mess. 100% functional gives strong guarantees. You can split up code horizontally (MVC), vertically ("apps"), but of you mix the two, you get a mess. I am working on a system which is 100% event-driven, and it works well in the context of this system, which is primarily about realtime data analytics. There are systems I'd build without any event-driven code either. There are hybrid systems too. There are architectures which are compatible (e.g. structured and OO), but many just aren't. Event-driven is one of those things which adds a lot of complexity to any system. Fully-embraced, that can pay dividends. A little here a little there and you have most of the cost and little upside.