It's always kind to apologize if the teams are unbalanced, or if something like that happens. There are very few people who can take loosing gracefully, and those people who can should be applauded for their good sportsmanship!
It's not needed, no, but a welcome surprise if it does come, IMO. It makes those people more likely to continue sticking it out and not RQ'ing, because they've had reinforcement that it's the right thing, and that other people appreciate it.
The only problem is if the other team suddenly decides it's sarcasm. Hopefully not, though. Good on ya for thanking them for sticking it out. This stuff makes the community better!
probably unneeded, but I usually make a comment if everyone on the winning side (whether I'm the lucky one or not) is all like "gggggggggggggggggggg" and there were players missing.
I also /clap upon winning and losing