Something else I noticed (though it is probably rooted in marketing more than anything else)
It was poetic in a sense that Goku landed the final attack in SSJ1. He and Frieza were almost exactly how they were during the battle of Namek, Goku shirtless with ripped pants and SSJ1, Frieza in his Final Form missing the end of his tail. Only this time side by side instead of facing each other.
At the end of the day, even with all the power ups and new abilities that Super has introduced, it was SSJ1 that dealt the final blow. Not UI, not Blue, not even god ki, but the most famous, well recognized, and reliable form. Against Frieza, Cell Majin Buu, and even Beerus, SSJ1 has been what Goku ended up in to finish the fight. Definitely a hit to the nostalgia factor.