Creativespiral said it really well.
WAV2Pro3 makes wavetable generation convenient by accepting 256-frame files directly from Serum. But the way it does this is by keeping every 16th frame and downsampling from 2048 samples to 1024. In other words, to meet the limitations of the Pro 3, WAV2Pro3 has to throw away almost 97% of the information it gets!
You can overcome this to a large extent by designing your wavetables in Serum specifically for the Pro 3. That is, create or add only 16 frames so that you have complete control over what gets into the Pro 3 wavetable.
Serum is the best tool available for creating Pro 3 wavetables, but using it for Pro 3 is a bit different than creating wavetables for use with the Serum synth itself.
I'm a bit skeptical about the prospect of scanning through a wavetable to approximate a 16384-sample cycle. For one thing, even though the Pro 3's frames are nominally 1024 samples, the 1024-sample set is only used at the very lowest part of the keyboard, up to around F#2. As you move up the keyboard, you're using 512, 256, and 128-sample versions of the waveform (Pro 3 wavetable sysex is so big because it really contains 64 waveforms). Also, scanning is going to be at a constant rate, not the variable rate that would be necessary to seamlessly link the waveforms together at different pitches. Plus you've got amplitude interpolation going on that you just can't turn off.
While some creative and dedicated programming might be able to get around some of these hurdles, my view is that it's probably fruitless to expect anything approaching "sample playback." Wavetable synthesis is a whole other thing, and it's hella fun when I'm not trying to make it jump through hoops. I treat sampled audio timbres more as raw material for synth sounds, with the bonus of motion.
And also, +1 for EG contour control.