I am a postdoc, just have been for quite a while (on four different grants at least). In Finnish academia it's not that uncommon to stay a postdoc even until retirement.
> That’s not true. If you make the hiring cut in you’re in for about 5 years of grunt work as an assistant prof.
For teaching and admin yes. But at least in fields I know, what research you do or whether you do at all is all up to you. Of course the risk is that you'll be unemployed after the assistant prof. term ends. My point is that if you don't care about that, you're quite free to do whatever research-wise.
> After PhD there will be nobody telling, and often not even caring, what to do.
If you make the hiring cut in you’re in for about 5 years of grunt work and committees as an assistant prof, right?
By “serious research” I mean the one they do for career advancement and hiring.