True enough, though most of the discussions I've seen since the playtest docs were released have centered not around bad mechanics, but personal preferences, such as healing and opportunity attacks.
Arguably, if a person feels compelled to change a mechanic, then for them it is a bad mechanic. Whether that's because it turns everyone else into the Wizard's sidekicks or just that they don't like it is largely irrelevant.
Conversely, the designers at WotC are good enough that very few objectively bad mechanics are ever likely to make it to the game, even at this stage.
In other words, pretty much all we have is personal preferences.
The playtest rules appear to be much easier to houserule than the more recent systems, which were much more tightly integrated.
It's really far too early to tell that (as indeed you noted in your post). But also: if 3e does 95% of what I want, but I can't readily fix the rest, while 5e does 50% but is easier to (mostly) fix, then I'm likely to look at it and decide against - I already have 3e plus years of experience with it; it's not really worth another $100 and dealing with the learning curve to have the chance to fix things.
Ultimately, on the issue of healing as-written, I'm with the OP - if that's all that I don't like with the system then I'll live with it, or fix it. My deal-breakers lie elsewhere. And, indeed, that particular argument is so well-worn that there's little need for discussion - a simple poll of preferences would probably suffice.
But it's very likely that one of my deal-breakers
will come up at some point, and it's equally quite likely that my issue won't be that the mechanics are objectively
bad, but rather that I will have a strong
preference for the alternative. I'd rather not have that discussion pre-emptively shot down by the "if you don't like it; change it" mantra.