Why would he tell her that? Clint has raillied his teammates multiple times (mostly Wanda), helped provide support in battles(stopping loki from chasing down and blowing away widow when she called for his help in A1, and not to mention you can go back watch their kill count and Clint has more chitarui kills than cap. Also likely the case for Ultron bots in aou) and distraction for his team in CW (keeping BP distracted while cap and buck flee, getting Tony off of Sam's ass after Sam called for his help), and most importantly single handedly keeping the nano gauntlet, the most powerful object in the universe at the time, safe from Outriders long before the portal'd backup heroes arrived. Had Clint failed, gave up, or gotten killed...they simply would have brought it to Thanos while the big three were getting their heads kicked in. And game over. Clint actively had a big role in saving the universe. There is zero reason the show would mention Kate being obsolete on the team as that's the point of the show...to show that powers aren't needed to be a hero. Clint knows she will help the cause just fine and has seen how capable she already is. And she likely will contribute just fine going forward. Glad they haven't addressed that nonsense.