...I need to stop believing that sewing up finished knitting pieces is any easier or faster than the rest of the sweater-making activity.
It's very finicky work. I've "invisibly" set in one sleeve (I'm starting on the sleeves, then sewing up the side seams) and it took 2 hours. And I don't think it's awesome work. Picking up bars on one side and stitches on the other is laborious. I don't care what the books say, unless you're an automaton - or the pattern works on row numbers (as opposed to length measurements) exclusively, you're not necessarily going to have the exact same number of rows on every piece.
Knitters: Can you corroborate that invisible seaming takes a lot of time and that you don't count stitch for stitch but just do your best to align everything? Of course, if you manage it with the aplomb set out in the books, be gentle when you advise me as much.