I remember the complaints that he wasn't proposing something specific before the election. So actually I don't think most people are aware that it is complicated. Otherwise they wouldn't have expected a simple solution.
People putting the onus on him to do the work and thought and research and discussion necessary to create a tentative plan and at least publicly present an outline of it does not imply they "expected a simple solution." In fact, the problem is precisely that Trump apparently literally thought that creating an Obamacare replacement would be so simple that he just didn't need to think about it at all.
Or maybe it is/was obvious that there are certain flaws in the US health care system and Obamacare that definitely have a better solution. There are other health care systems in the world, so it is obvious that Obamacare is not the only possible way to do it.
You're absolutely correct. There are many problems with Obamacare and there are many other systems we could have. The very same people licking Trump's boots now are the ones who previously shot down every proposed solution and better system when others suggested them in the first place. Which led to the compromise (not as good as it could have been) system we have now.
The issue at hand is that Trump is either willfully or unknowingly ignoring that he and his people are the ones who actively prevented us from having a better system. And the only reason why they're only now acknowledging it's a hard problem, is that now they're the ones who have to fix it.