I find xterm works great with tmux plus I can easily change font size on the fly without any issues. Change font sizes on other terminals is either not allowed or sometime (rarely) corrupts the display.
But what I do notice is that xterm is the only program that shows things like ncurses (i.e. mc, tree, etc.), and tmux, and language/locale correctly on everything.
I can get 1-2 of the above items but never all of them. (Konsole does a great job too, but xterm opens faster on my i3 setup.) I've manipulated my various dotfiles, and tried multiple combinations but xterm works 100% of the time.
But maybe you don't care about that. 90% of the time, I don't.
I don't want my servers to be cutesy.
Other TEs, especially libvte-based ones, are more like crappy xterm emulators.
So there are reasons to want xterm, specifically.
Other terms as you say, suck.
BTW, does this work under OpenBSD and ksh with "set -o vi"?
It starts up fast and reads text comparably fast, and it works great with most console programs. It doesn't try to reflow text when resizing, which simply can't be done correctly. Most other terminals try to reflow and it is frequently a mess (last I checked is long ago)...
Another reason I like xterm is that it's one of the few left that support bitmap fonts, and on old low-res screens those are much better legible. (On more modern displays with DPI > 150, it starts to become difficult to find large enough bitmap fonts.)
You can also set .Xresources, but that's a bit more complicated.