I think your " built to fail " argument isn't more than a cheap talking point. It was a plan that tried to help the most vulnerable but lacked fiscal responsibility and had a very sloppy roll out.
When Obamacare was first coming out, I must have heard a dozen experts on television giving it a year by year analysis of the roll-out, when various stages would kick in saying that this year when it was fully implemented it would collapse and that the inevitable result would be single payer, and that is pretty much exactly what has happened and where it is going.
.. however it had and still has the ability to be amended and tweaked and improved. There has never been a bipartisan attempt to fix the areas that were not working. A lot of empty promises and political posturing from the right to do something that they obviously were not prepared to do.
Anything has the ability to be amended and improved. Question is, what is easier, trying to wade through the 30,000 pages of Obamacare or just starting from scratch? There never seems much interest or hope for any bipartisan effort these days and I would say that more of that seems to come from the Left. They may throw it out there for optics, but when approached, their idea of "cooperation" is not to meet the GOP in the middle but for the GOP to come fully onto their side and do everything their way.
But I agree with the rest of what you say: the GOP has admitted that it was pretty easy to vote to repeal Obamacare when Obama was in office because they knew he would never sign it. They didn't expect Trump to win, and were caught with their pants down. And there never is any unity, they always have 5 or 6 hold outs no matter what, as if they are determined to see the party fail. They damn well get it together and get something done. People like Paul need to start considering that fixing some of the healthcare issues so they can move onto tax reform is a lot better than leaving healthcare totally broken as it is, breaking a major promise and not reforming taxes either!