The highest percentage of drafting a starter in the NFL draft comes from the first three rounds.
The Saints legendary 2017 draft class:
1st Round - Marshon Lattimore
1st Round - Ryan Ramcyzk
2nd Round - Marcus Williams
3rd Round - Alvin Kamara
3rd Round - Alex Anzalone
3rd Round - Trey Hendrickson
6th Round - Al-Quadin Muhammad
Notice a theme there? Coincidentally the 2017 draft class was the last time the Saints had more than three picks in the first three rounds, and since 2017 the Saints average 2.4 picks in the first three rounds per draft. Meaning they're trading away picks with the highest percentage of becoming a starter more than they're acquiring them.