True, speed does matter somewhat. But even if xterm isn’t the ultimate in speed, it’s pretty good. Starts up instantly (the benefit of no extraneous libraries); the worst question is if it’s occasionally limited to the framerate for certain output patterns, and if there’s a clog you can always minimize it for a moment.
Speed is far from the only thing that matters in terminal emulators though. Correctness is critical.
The only terminals in which I have any confidence of correctness are xterm and pangoterm. And I suppose technically the BEL-for-ST extension is incorrect even there, but we have to live with that and a workaround is available.
A lot of terminal emulators end up hard-coding a handful of common sequences, and fail to correctly ignore sequences they don’t implement. And worse, many go on to implement sequences that cannot be correctly handled.
One simple example that usually fails: \e!!F. More nasty, however, are the ones that ignore intermediaries and execute some unrelated command instead.
I can’t be bothered to pick apart specific terminals anymore. Most don’t even know what an IR is.
“Freedom to take away others’ freedom” is not actually freedom.
From my experience, Cinnamon is definitely highly immature compared to KDE. Very poor support for virtual desktops is the thing that jumped out at me most. There were also some problems regarding shortcuts and/or keyboard layout I think, and probably others, but I only played with it for a couple weeks while limited to LiveCD.