Horvat is a 2c offensively with mediocre defensive abilities. He is like a Koivu who can't play defense. We already have a 2c that is a great defensive player, Hartman playing like a borderline #1C, and Rossi ready for primetime. Oh, and Hartman and JEE's cap hit together will cost about the same as Horvat's new deal, which will start in 23-24.
I can't imagine a more short sighted trade.
Trade Dumba for futures, let CO be king of the hill for next couple of years till injury and bloated contracts drag them down, then unleash the hounds in 25-26. Adding Horvat minus Dumba now will not make a significant difference to the team, especially once you factor in what his new cap will co to our cap situation.