Stronger personas have better skills which makes them better fodder for gallows, and you can't instakill most personas when you enter a palace for the first time.

I do all of my fusions in palaces on the first or second day. Instead of running around and resetting the game I can just get loads of money in a few encounters and then grab whatever persona I need.

Maybe we have different play styles and that's why you think Yoshida is bad but he's extremely useful for most other people regardless of play style because he gives the most options for getting personas or for farming money and items, which is why he should be considered on par with the twins.