The price isn't the problem, having someone reasonable hosting my email is. IMO electron apps are the biggest waste of time out. Our browsers can do this already. So I don't see the point, or it being reasonable.
Electron is the most cost effective, least wasteful way to produce a desktop app on all 3 OSes. They’re providing a feature to people who wanted it, while wasting less money from ungrateful customers like yourself who don’t care. It’d cost much more to build & maintain a native desktop app when electron works just fine.
Fastmail are an awesome developer, JMAP is great, their mobile apps are great and actually offer some reason to exist, and I like their ethos as far as I can tell. None of this detracts from the fact making an electron app that does nothing other than shell a website, in nearly every case, is a waste of time.