While Omnisphere has OSC's A to D, you can consider that Rapid is having 8 (triple) oscs (confusingly named as layers) from A to H and that's all (no multi outs, no midi channel routing, no true multilayering).
I say "confusingly" because often time this number of oscs is simply overkill and is somehow "inviting" to think true multilayer (like omnisphere) and leads to frustration.
Also, I'm not at all for "one preset does it all" kind of strategy because you simply can't get inside (any) the synth the processing required for releasable music. So when I use Rapid, I pretty much use 1 layer, and maybe more when programming pads (and I add various layers of movement).
Paradoxically, lately I found myself staying away from Rapid and Avenger and go for Diva, Serum and Ableton's own instruments (and Falcon, for it's freaking awesome envelopes, but I literally go with the timer on the desk, I set 10-20-30 minutes and at the contdown I go with whatever sound I have so far) - I find that "limited" synths drastically (I mean hours less!) improve my workflow as I don't get lost in "endless possibilities".
So yeah, while a synth may be a "sound designer's heaven" it's also a music producer's ultimate procrastination tool