It is really rare for this conversation to happen to a 3 year starter. Last I think of is Chris Simms.
Here is the PFF grades for the remaining QBs in the playoffs.
8. Stockton: Offense: 57.6Pass: 54.7Run: 61.6Overall Rank: Not ranked
7. Ewers: Offense: 72.0Pass: 71.2Run: 56.2Overall Rank: 154
Ewers is either really good or he's getting benched in favor of Arch Manning. There's no in between. For the season, Ewers has 2,867 passing yards to go with 28 touchdowns, but 10 big interceptions. Texas can go all the way, but only if Ewers is on.
6. Maddux: Offense: 75.9Pass: 72.1Run: 69.1Overall Rank: 110
5. Howard: Offense: 84.2Pass: 84.2Run: 61.7Overall Rank: 43
4. Allar: Offense: 85.5Pass: 82.2Run: 75.0Overall Rank: 35
3. Leonard: Offense: 85.6Pass: 75.9Run: 83.2Rank: 34
2. Gabriel: Offense: 89.9Pass: 89.3Run: 63.3Overall Rank: 16
1. Leavitt: Offense: 90.1Pass: 85.6Run: 78.1Overall Rank: 15
Ranking the 8 remaining quarterbacks in the College Football Playoff by PFF grades