I can answer this - it's partly the first two, but also that the default FP physics are bobbins - there are too many elements that don't behave in a realistic way. I still use VP 9.9 as a design tool, with my own set of accurately-built custom objects, and custom physics routines in the script. It still isn't perfect of course - VP's physics timer runs on cycles that are long enough to eventually predict, and it doesn't allow for skips and air balls unless things go seriously haywire.

At Heighway, when myself and SlamTilt would come up with intriguing ideas, or wanted to prove a concept, what would happen is one of us would build us something flippable in one engine, and the other would present it in the other engine - me in VP, him in FP with his own settings. Anything that after some tweaking flipped well in both versions, we could be pretty sure we had the best of both worlds and it ought to translate well to a potential whitewood. We built up a fair library of unused designs between us this way.

Saucer-lipping has been part of my custom scripts on tables for years, as is drop targets sweep physics, magnets, impact-type captive ball brackets, vari-targets and spinning posts. That's the other advantage of VP over FP: the ability to read the velocity and position of every ball on the playfield in real time, and directly manipulate those values in the script to create realistic interactions with other objects.

Was Napstablook in there, sneaking a quick go with the phantom switches?