While, I haven't been as many times as you, I would hardly call myself a "newbie". We had many trips using the old fastpass system. We've had two with the new system. I take offense at your implication that if I like the new system, it's because I don't know any better.
You get offended pretty easily.

How I take the comment is that if you never used legacy FP, then you would not be able to compare a prior experience to FP+ and FP+ may seem great to a newbie because they have no comparison.
I'm not a newbie but even if I were I would relate to the OP regarding FP+ in many ways. For example, at one point last week I would have liked to change our schedule and visit a different park on a different day than originally planned. To do so, I would have lost FP+ scheduled 60 days out and the headliners were gone according to the site. Instead we sucked it up and continued on with the original plan. At another point, I went to a Kiosk and tried to get more FP after scheduling/using the first 3 early hoping more would become available and only 4 choices were left in MK and none were desirable at all.
We even did rope drop and did not get to ride as much as we normally would have - because FP+ dictated our every move (we had to make it to the next one on time and of course rides are not next to each other per say) and we did not have time to do repeat rides or did not want to chance getting back in line if we wanted to use FP+ for another ride in time. We had to rush lunch to meet our last FP time, the restaurant was so slow serving our food which is hard to predict 60 days out. All of this while still happened even though we laid out the park maps and planned dining times, etc. when choosing FP+ to ensure we weren't running back and forth across the park.
My overall opinion is that while FP+ could be cool technology if maximized in it's use, legacy FP was much better. With legacy you weren't so restricted and we got more done. Too much over planning with FP+. With legacy, there was spontaneity as I chose the rides I wanted, where I wanted and when I wanted and if they were out of FP hard tickets then they were out. FP+ did not ruin our trip by no means but we didn't have any circumstances crop up that interfered too much with the times scheduled (if I had small children I would have probably had a bigger issue with it).
What determines a Legacy FP or FP+ fan? It probably all depends on what your touring style is. Our touring style is to get there at rope drop, primarily do all the rides and do some more than once.