I think it’s fair to say that Tagoma would have been destroyed by First form Frieza.
First form Frieza one shot Gohan, who while not mystic still had some power to him.
Then Gohan goes and “trains” and becomes mystic again. So he’s back to Tagoma levels of power. Even if you say that somehow, he became 100 times stronger than he was in his old mystic form, even though he didn’t demonstrate any kind of training that would justify such an increase, he would still be fodder to Friezas last form.
Then cut to the tournament of power, and Gohan is doing far too well again far too powerful opponents.
Not all of that was related to the thread, just talking about DBS.
Don’t even need to talk about any of the human fighters.
Not to mention that Gohan was able to go Mystic in BoG just fine... but somehow, in the time between BoG and RoF, he "forgot" both how to go Mystic and even how to go SSJ2.
And yeah, like you said, him training with Piccolo, re-learning Mystic and suddenly being able to go toe to toe with SSJB was dumb as f*ck.
If Gohan was learning to get god ki under Whis, or maybe training in the RoSaT or something I could've bought it, but just training outside for a few hours with Piccolo and he reaches that level? Yeah, okay.