2.) You simply won't learn much. Now, that is not a con for some people. In fact, that is a huge pro for most people, cause you have amazing sampled base to build upon and thousands of great patches for instant use if you don't feel like tweaking. But you're still most of the time creating a form of derivative work. It's derivated from Eric's amazing collection of sounds, but still. You do it, because you can and it's comfy. Without it, you'd be forced to go out with a recorder and make some foley sounds to stuff into your granular synth.
That's the reason I've chosen Falcon in the end. For NOT having the sample library, because that way I'm forced to learn how to make my own. When I'm doing a lightbulb patch, I want it to be my lightbulbs.
)
I'm not bashing on anyone who loves Omni. I get it and there are tones of reasons to do so. I'm just in love with making your own sounds, so Falcon made a bit more sense to me actually. And I can't afford both.
So for all the Omni users, if you're still a bit of nerd too, don't forget to drop your own sample into it here or there.