If you do copy on highlight (no need to press ctrl-c or similar) its pretty broken.
eg. create a split so you have 2 sessions on the screen, highlight text in split A, then highlight text in split B it doesn't un-highlight the text in split A.
There are also times when highlighted text doesn't make it to the copy buffer for whatever reason.
Yeah, I do use "copy on select" since mIRC/Putty days.
Coming back to split - checked, thanks!
For me, who prefers having separate windows, not splitting by means of terminal (splitting in tmux on rare occasions though), it's natural to act those independent on selection, giving me visual hint on what I was working on - I see it more as advantage.
For tabs I don't care much as not using them.