You probably can’t get the count “XY” without heavier coding, but adding this custom CSS should improve your situation:
dd.groups:last-child > a::after {
content: 'and more';
}
I haven’t tested this CSS exhaustively throughout the site, but in a spot check it seems to act only on the groups link on the profile page. Please advise if appears somewhere it doesn’t belong.
(Also, I do agree that the discoverability of ... isn’t great, and a change along these lines in core would be welcome.)