Cooper is more talented. No denying that. But Cooper's production in Dallas is not that much better than Gallup’s 819 yards plus 5 TDs average per season.
Cooper averages out to 850 yards / season with an average of 6 TDs.
Is it worth continuing to pay $20+ million/year for a WR when your #2 WR has similar production and could be kept for cheaper?
CeeDee is averaging 82 yards receiving/game (currently leading all Cowboys receivers with 497 yards and 4 TDs), while he's on pace to catch for over 1,400 yards and at least 8+ TDs.
This is after CeeDee went for over 900 receiving yards and a team tying 5 TDs last year his rookie year. Clearly, CeeDee is becoming or already is this team's #1 WR.
If Dallas sees themselves in a position where they may be forced to make big contract cuts after this season, Cooper might be the odd man out.