Why would Love / IT be a better defensive combo than Love / Kyrie? We'd get killed defensively, and I'm wary of Love being able to carry the offensive load.
Being surrounded by better defensive players in a better system would surely help. Brad's system did a decent enough job of hiding IT defensively and somehow preventing him being posted up by every bigger point guard. Also, not everyone will be able to abuse the 1/4 PnR like Golden State does so masterfully.
I think it's also important to note that we have some of the absolute best defenders in the league with regard to versatility. Surrounding Love and IT with versatile defenders that can switch onto multiple positions like Amir, Crowder, Smart, Bradley, and JJ helps out a lot in hiding those players compared to being surrounded by players like Smith, Thompson, Dellavedova, etc.
Further, if you'd add another scorer to the lineup, e.g. Butler, Durant, Cousins, etc., then you could legitimately move IT back to the bench to avoid this issue for large portions of the game, while also boostering the bench.