I think the joint practices are more important than preseason games. In joint practices, teams can work on things they need to improve or want to see where they are at.
In preseason games, you aren't going to get the starters to play all that much except in one game anyway. Even when there were four preseason games, the starters usually played a series the first game, maybe a quarter the second, and a little more than a half in the third, and sat out the fourth. And you cannot control what will happen in those games and what the other team is doing.
I think they should keep the joint practices but teams should make their starters play a half of football in the first or second game.
Personally, I don't think it is the joint practices that did away with starters playing the preseason. Joint practices have been going on for a decade before this practice started.
I think it is the 17 game season that did away with players playing in the preseason. I think it is coaches not wanting their players burnt out because the season is longer. Combine that with most teams having to play overseas which just adds more stress to players' bodies.
If they go to the 18 game season, there is no chance you are going to see starters play in the preseason.