I have not, and why someone would want to I do not know, though I am sure someone has… lol
H4 has the capability of sounding much like the Prologue.
No, but the basic waveforms are available (plus more).
E.g. All waveforms (Sine, Triangle, Saw and Square) are available (as basic oscillators) in forms of sync, cross modulation and xor. I.e. without the need to use additional oscillators, each oscillator can produce sync-sounds, FM like sounds and ring modulation like sounds, respectively.
No, it is not the same synthesizer with a different GUI.
The complexity of HALion 4 goes way beyond that of Prologue.
As mentioned above H4 has more filter modes (single, serial, parallel, various morphing) and shapes (24 currently), envelopes with 128 nodes (compare to a traditional ADSR envelope which equals 4 nodes), polyphonic LFO’s (i.e. calculated per triggered note), each voice (a.k.a. zone) has three oscillators, a sub oscillator, a separate ring modulation and a noise generator, up to 8 voice unison, etc. Furthermore, a program is virtually limitless in the amount of these zones (voices) you can have.
Well, from the above you should get a few hints to the difference. If you want more, you can download and read the Operation Manual, which is available under Steinberg support for HALion 4. Tons of information in it.