particularly if you are in a situation where you need to X-forward a browser session over the internet; Chrome and Firefox might be particularly painful while Konqueror could be usable.
Neither Chrome nor Firefox's bloat is drawing on the desktop
You're probably correct on that, in that those browsers are just simply bloated, period.
and in any case the performance of the window draw will pale in comparison to sending a bitmap of the website you're currently visiting over the internet.
From my experience that is not the case. I have had times where I have used XForward to send browser sessions across the internet before and there have been profound differences in the initial loading of the same site between firefox and konqueror. From my experience konqueror was faster to the point where I could start the browser, load the page, get what I needed from it, and close the session in less time than it took just to get firefox to open and accept an address in the address bar. This was with no flash or other fancy plug-ins loaded on either browser, connecting to the same PC on the same cable modem either way.
I don't know that maintaining a web browser in the face of Chrome, Firefox, Edge, Opera and the rest makes any sense?
I can tell you from experience that Konqueror is a browser with a vastly smaller footprint than Chrome or Firefox. There are times when this can make a really big difference, particularly if you are in a situation where you need to X-forward a browser session over the internet; Chrome and Firefox might be particularly painful while Konqueror could be usable.
Opera I haven't used in a long time, and the last time I tried to use it I found it quite broken in *nix. Maybe it's better now? As for Edge, I'm not aware of a system upon which you could have both KDE and Edge. If you know of such a beast, feel free to enlighten me.
Also, a standalone mail client? I haven't used one of those in nearly 5 years now. So, do I care that it hasn't updated? Do its users want it to become more like Outlook? I think probably not.
There is still demand for a standalone mail client, though I can't say I've used KMail much. I use Thunderbird religiously. I most certainly do not want it to look any more like Outlook, in fact I value how much it looks like the old Netscape Communicator.
My gripe with KDE the last time I tried to use it was lack of font scaling support for 4K screens.
Holy first world problems, batman. If I ever find myself with that much disposable income