I think the main reason Umino is being rejected is because everything looked like he would be coming back from excursion with a real edge to him, a chip on his shoulder -- the Roughneck, the apprentice of Moxley, the Death Rider.
People expected like a denim vest, a taciturn expression on his face, and a hard, no-nonsense kind of gimmick.
And we got Tanahashi-lite-lite. Tanahashi with too much milk and too much sugar. Pink? He's wearing pink and white? Why? He came back looking to Tanahashi what Voyager was to The Next Generation.
It was just so out of step with what everyone expected, what seemed to be the obvious set up for his return gimmick.
It's such a head scratcher that it makes the conspiracy theorist in me wonder if Gedo isn't trying to deliberately engineer another Naito through a failed Stardust Genius like flop.