I feel like this is a very scoreboard driven kind of thinking that misses the forest for the trees.
What we have learned is that Ten Hag can coach teams made up of very raw kids and past-peak veterans to play effective attacking football in the style we want, and he can get them to play that way against much bigger, more talented teams. He also can get them to press really well and play a very tight defence, without having great centrebacks.
Pochettino struggled to do that by the end of his time, so Ten Hag might be able to at least bring us back to where we were, or even take us further.
If you spend all day just looking at final scores then you miss the point. A coach has no influence on the final score. He cannot kick the ball, can’t make a pass. He can only train the team before the match, shout advice, and make 3 substitutions. The only thing he is responsible for is the process. That’s what he controls. So you need to evaluate him based on that.