The question is not so much is he good enough, but whether he can become good enough.
Even with better accuracy and decision making, he's not going to be an "elite" quarterback.
But the NFL is full of veteran quarterbacks who have better accuracy and decision making, and have never made the SB - Dalton, Stafford, Rivers. Just to name a few.
The Cowboys thought, based on 2016, that they could re-invent the 1990 's SB winning teams, since Zeke won the rushing title, and the o-line was dominant. So they decided to go with Dak, since they had him for 3 more years at a very low cost, letting them sign o-line guys like Martin.
But then Leary left, Collins didn't live up to expectations at tackle, Frederick got an illness, Smith's back limited his practice and playing time. The grand scheme all fell apart.
So where to go from here? If you go with somehow drafting nos 1-3 and get the next Mahomes, you need receivers to fit his skills, but you're locked in with big contracts to Martin, Smith, Lee, etc. Probably have to add Lawrence to that list after this year. Where's the money coming from? Better hope the cap blows up sky high the next 2-3 years.
And that's IF your next Mahomes doesn't turn out to be Ryan Leaf, Matt Leinart, etc.
Just saying that you can get rid of Dak, but there's no magic formula to win SBs. If he goes, better hope JJ, SJ and JG get a whole lot smarter than they are now....