Against teams playing 5 out or small ball lineups Uncle Luke has become quite useless tbh. Shame cause he started off the season as maybe the best backup big in the league. Hopefully Plumlee is serviceable against those types of lineups.
No big is useful against those small ball lineups. That's why they run it. The Spurs have more than enough players to be able to counter small ball lineups. Leaving Kornet in would be stupid.