Well, yeah, resentment. Vegeta didn't pledge to reach some arbitrary higher plateau; it was specifically UI, and specifically before Goku. It didn't turn out like he wanted so his resentment bubbled over. Just because he's had greater displays of it in the past doesn't mean that's not what this was. Plus the insecurity. Perhaps a little disillusionment. I don't mind, myself, but I see why some people think it's a regression.
he's had greater displays of it is why this doesn't qualify. People seem to think that just because Vegeta acknowledged Goku as stronger than him in the Buu arc that it meant he'd give up on being his own person, give up on surpassing Goku and give up on training. These aren't true. He'll still try his best to do all these things; he just won't be a planet-risking, self-destructive prick about it anymore.
Let's put it this way: Vegeta didn't say he'll quit drugs. He said he'll quit heroin and transition to marijuana, essentially. Yes, he's still taking drugs, but a FAR less dangerous and destructive kind. He's no longer going to think of Goku as low-class trash, but he is still going to try to surpass him, which is a healthier rivalry.
He doesn't hate Goku for surpassing him; he's angry at himself for forgetting the principles that got him to the dance in the first place. There's nothing wrong with this. If you disagree with Vegeta's assessment of his situation, then that's fine. But the minute you try to say this is bad/regressive/hackneyed writing or something, you've gone way too far in that direction. It isn't bad writing because it honors what came before while presenting the character in a light that makes sense.
He can insist on his own way, but believing that going it solo is why he's at this dance...can't say it's definitively wrong since we'll never know, but nothing leads me to believe he would have obtained god ki and beyond on his own, and I think past performance indicates he wouldn't have.
He explained in this chapter all the times going it alone has benefited him. It was as a lone warrior on the battlefield that he became powerful enough to toss around Goku, Gohan, Krillin and Yajirobe when he first came to Earth. It was as a lonely warrior that he achieved Super Saiyan and beyond.
I don't recall if the manga outright stated this or not, but the anime said in explicit terms that Vegeta somehow achieved God Ki on his own through training rather than a ritual. Goku praises him against Frieza for being able to do so.
Like I said, I don't think a word he said is worth taking to heart. It's not his philosophy, it's just a tantrum that will die down and he'll go back to normal.
It is absolutely his philosophy though. Vegeta has always been loathe to ask for help. He hits his head against a brick wall until he gets through. The only thing that's changed is that he's less self-destructive about it.