Frieza is an entirely different matter. He was a prodigy with the highest power level in the universe amongst mortals (except Buu... which was a demon anyway) without ever training. He built a galactic empire based on his strength. After he trained to pursue his vendetta, he unlocked an entirely new transformation that gave him immense power but he couldn't really control it and ended up losing the fight against both Goku and Vegeta. He was the main enemy of that movie/arc and still had
some drawbacks.
Trunks' power up was an asspull as well, but the false ssj blue was rage induced, and we have other examples of what rage can do (Vegeta hitting Beerus and trashing Black, Goku beating Black and Zamasu together, Black causing a distortion in space etc, likely even Freeza achieving his golden transformation was a combination of trainingr+pure rage), while the second one was sorta like the genkidama.
But Frieza's drawbacks only happened because he rushed after 4 months of training. We're talking
13 years here for 17.
17 was a lot stronger than Frieza without ever training too. He was stronger than Piccolo, the Super Saiyans, Frieza and his dad, and cell (that had to absorb millions of people to surpass 17).
He only got beaten thanks to time travel shenanigans. Which robbed him from his chance to try to get stronger.
Trunks got angry plenty of times though. More notably when Mai "died". Also, Trunks was putting up with SSR Black before actually transforming.
But even then if you consider that it's OK to have asspulls because "it's the saiyan thing to get angry" then just accept that it's the "androids" thing to be easily better than them, at the cost of not getting transformations (not that they're any useful

).
Maybe there's also the fact that 18 was always in the anime and she never got really much stronger than she was, that too might alter perception of what an android can do, but either way it felt weird as hell. The scenario of the fight at sunset was kinda cool though.
18 never cared for fighting, she cared about fancy clothes and money. 17 was the fighter.
The way they trivialized previous trainings/enemies has always been my biggest gripe with DB, easily.
Still, the point is that in this tournament there are fighters that are incredibly less powerful than 17 was in Z, and they will certainly have their part during it (the tournament is about team work after all, and other than spending lots of episodes on secondary characters the anime already showed how good U11 is at this), so was there really a reason to make 17 around ssjb level and break suspension of disbelief like you said? SSJ3 is pretty damn strong, and nobody would've said anything if he was even considerably stronger than that. It would've been completely credible.
Because they need heavy hitters in the duo/trio.
Gohan, 17, Goku and Vegeta. Then the rest will have the special techniques, and the strategists etc...
You can't have only 2 god tier people when there's hit , Jiren, Toppo and Brola.
Plus we are finally moving past only Goku and Vegeta being relevant against the strongest people. Finally. And an earthling does it at that. Personally I'm glad. I'd rather focus on fun, cool battles, nice story boarding / artistic direction and great cast with variety in their personalities, looks and fighting styles, than whatever "credibility" the power levels had. Super was awful on that front from day one, it got worse while everything else got better, the pros far outweigh the cons IMO.