I think Kempe is solidly a middle sixer who is playing a good complementary top line role, it's not just anyone that can play with Kopitar as we've seen so there's big value int here when we find it.
re: Kopitar vs. Toffoli I'd say TT is the 'better player' but Kempe is a swiss army knife like Lewis was with better production--the guy is a monster forechecker with oodles of speed, hands, and can be instantly deadly; he can lug the puck through the neutral zone in any situation; he'll get his nose dirty and take fair fights. He's become a much more well-rounded player than I ever thought he'd become, he's headed for about 50 points which is what I figured his ceiling was as well--provided he keeps up this season (biggest criticism for me was always consistency, even more so than IQ--but his read of the game has become really strong), he'll be at the top of what I thought he'd be capable of and a really really good late 1st selection.
I know like
@Frolov 6'3 says some people were dead set on him being a 1st liner/60 point guy but that's early first talent, there's a reason he was still available late, and have to adjust expectations commensurately.