Given a high-quality (good UX, etc.) web-based client would be available, would you consider switching?
A native application has advantages over a web site, a web app, or a "native" app built using Electron, etc:
* in resource usage,
* in UX consistency,
* in integration with the rest of the system, eg. for scripting (Apple Script), accessibility, etc
* in working with locally-cached emails while offline or with degraded connectivity,
* in having no ongoing cost,
* in being vendor independent,
* in supporting the use of standard protocols (SMTP / IMAP), rather than a proprietary web backend API
and there's probably more I could come up with if I thought about it some more.
A web application (not an Electron app) has one primary advantage: it can easily access significantly more computational and storage resources than my laptop can. That could be an advantage for searching. There's probably other advantages I could think of with more time here too.
So, while I'd be happy to consider a web-based solution, I think it's fair to say that I think the deck is stacked against such a product, for my purposes.