“In all these cases of separating starter plants, it’s a bit tedious to not damage the roots too badly...”
If the root ball is sopping wet, it makes it easier to separate the individual plants, but a very sharp knife on a dry root ball works well, too. ;)
Yes, I usually get them “sopping”, to use your word, before “separation”. Not too long of course! Just a few hours, and then the plant has a little “reserve” to work from, hopefully. Then they do pull apart more easily. In a couple cases where roots have REALLY grown together, and I can’t get them apart without risking the stem of the plant, I’ve cut them apart, as you say, but it seems like the survival rate was less. I don’t recall what those plants were, though - not tomatoes, I think...
Thanks!