Eh, there were like three separate instances where Gohan's "Hidden Power" was released. It's like every time he needed a power-up to become relevant, the series just pretended that Gohan hadn't already tapped into that power.
Then there's Goten/Trunks going Super Saiyan at such a young age; Toriyama wanted them to be relevant, but logically there's no way that their power-level should have been that high.
Also, Saiyans growing stronger from near-death experiences (including self-inflicted wounds like Vegeta's during the Frieza Saga)... why not just constantly hurt each other and eat Senzu?
Dragon Ball has always just made shit up as it goes along. It doesn't follow a rigid set of rules. Even the means of awakening SSG is pretty similar to Trunks' recent power-up; out basically combined that with the spirit bomb. And gaining power through emotion has always been a thing since at least SS1.
Trunks was always going to land the final blow; this is his arc, despite Goku/Vegeta sharing the spotlight.
To become relevant? Your assumption is from only one point of view, a childish one. Gohan was naturally born stronger than Goku and his hidden potential was no secret at all. Goten and trunks was probably given the SS naturally without need of training because the breeds potential seemingly increases by generation. I have nothing against that from my aspect, the saiyans get senkai boosts because they are saiyans. The longer they fight the stronger they become,
they are a warrior race.
The SSG awakening is not to be related to this ridiculous asspull that trunks did, lmao how exactly do you define Trunk's emotional spirit bomb as logical? First, the spirit bomb can
only be used by those who mastered the technique not by just automatically getting the feeling of it. And akira clearly was out of his mind when he chose to end it like that, the genkidama(spirit bomb) is meant to be gathered by a fighter when you request the energy. Trunks did not utter a word, and yet the energy was flowing from the people for no reason.
"gaining power through emotions" is heavly exaggerated by akira, i accept and understand how a emotion triggers the legendary saiyan transformation. And emotional power ups are common in saiyans, BUT there is no logical reason for trunks massive power increase when he fought zamasu black. Seriously? how can someone expect me to belive such rapid change. Trunks did not train as harsh like Vegeta nor Goku did but he still pulled off that BS. If that's akira's way to make someone relevant in DBS and heroic then i'm doubting his memory.