They've only mentioned it on two separate occasions though as far as I know. First time after she beat him and then during the Elseworlds crossover. They did mention her being stronger twice during the crossover, though one of the times was just Clark replying with "you would've been fine without me" or something like that after they took down Amazo, and then in the Supergirl episode when he says he's leaving he says the world doesn't need Superman when it has Supergirl.

These lines don't feel in any way like they're trying to push the idea that Supergirl is stronger in our face as I've seen some other people have been saying. I didn't in any way feel like it was out of place or anything.

These same type of lines have been said countless times between two male heroes without anyone having any issue with it. I can remember moments where Oliver tells Barry something like "you would be fine without me" or "you're a greater hero than me" and same interactions between other male characters that no one brings up because "it's normal for a male character to acknowledge another male character is stronger than them".

It shows how insecure supergirl fans and writers are

I would argue that it's the opposite where so many people online are going on about how "she's stronger when she's not supposed to be!" it just shows how insecure so many people are that they're freaking out whenever they're presented with Supergirl being more powerful than Superman.