they dont scale to their main time line counter parts though. if you remember back in Z, trunks stated that android 17 and 18 were much stronger in gokus timeline then they were in his own. things dont "scale" from time line to time line
Broly also wasn't canon back then, and Trunks wasn't running around defeating gods
I don't think we should base whats currently happening in the series to what was written almost 30 years ago.
Trunks does scale because he isn't scaling to his own timeline, he grows stronger when he jumps to the past with Goku & co. So his power scale is based directly in comparison to U7.
From the Cell saga to the Black Arc. He gained his power when fighting in U7's current timeline, not when he went back to the future
So that means whenever we see Future Trunks, we know he will be fighting along side Goku and Vegeta, against an opponent that is much stronger than in his timeline, so he will gain a power up - and he usually gains one that scales him not much further behind than his father, who is stronger than everyone not named Goku.
Trunks has always been the #3 in power, even if you look back at the Cell saga. Vegeta AND Cell even admitted themselves at separate points that Trunks was stronger than Vegeta. So if we line everyone up, that ranks SSJ2 Gohan, Goku, then Trunks, Vegeta, etc etc.
Hendrix has always been top tier b