Toyotarō was initially a dōjinshi artist working under the name Toyble , and notable for creating a Dragon Ball AF manga in the 2000s. He was hired by Shueisha in 2012 when he requested being the one to draw Dragon Ball Super  and debuted his career as an official manga artist under the name Toyotarō. He created the manga adaptation for the Dragon Ball Z anime 2015 film, Dragon Ball Z: Resurrection ‘F’ , titled Dragon Ball Z: Resurrection ‘F’ - Special One Shot . Toyotarō drew two pages of Dragon Ball Super as demonstration, and Toriyama chose him as his successor.
“New training methods to increase a character’s base form so that the already existing multipliers make them even more powerful” That’s literally what God Ki was, and that was necessary. Again, Goku hit his max base power back in Cell Saga and since only was able to get forms to forcefully progress. Something big was absolutely necessary to increase base form naturally passed that limit, they couldn’t just train a bit more, something huge and beyond mortal power was absolutely needed to make that happen, that’s what God Ki did which was incredibly important. You’re saying that could have been done without a form, which sure it could, but it wouldn’t have been anything close to impactful as it was with a form to accompany it. Even better was that the form became surpassable by base form so it was a temporary form who’s power was necessary but didn’t add to a continuing stack of transformations. SSJG itself was necessary, Goku needed a new form and new base power. It would have betrayed the style of Z to not do this and not gonna lie, without this new form the powerup would have been far too arbitrary and honestly? Boring.