Uh, so how do you explain it being quantized perfectly to a grid no matter the BPM? It's because the hits are moved around to fit. What you're saying may be partially true, but then you'd be stuck with whatever speed the so-called human played the beat at. There has to be grid manipulation of the samples to make it fit for any situation. That takes away whatever human feel the real human had when recording it. So you have to re-humanize it.
The packaged grooves are played by a drummer.
They take all the recorded performances and break them up into 1-2, sometimes longer, measures and package them as a variety of grooves...and they also convert each audio beat into a sample.
When you move the beats in MIDI, you are simply giving the sample a new play command.
Yes, you move the beats manually, you change the original groove...but, you can use the "humanize" options to maintain that random, human feel.
The grooves are also categorized by the original BPM...so if you stay in the ballpark, it will sound fine even if you change the BPM and/or move some of the beats around.
If you take a slow groove that was recorded at say....68 BPM...and you ratchet it up to 140 BMP....it will sound weird....which is why they provide so many different BPM grooves and often a lot of variations.
Like you don't want to start with with an uptempo 4/4 rock beat, and then turn it into some slow shuffle thing. You are better off going to the section that has the shuffle grooves and find something close to your BPM.
If you looked at Superior Drummer (which is what I'm basing my comments on, I don't really use EZ1 or EZ2)...you would see that it is VERY mix focused, just like a typical drum tracking session would be. You have the same audio options...plus, you can fuck around with the beats.
If it were a real recording of a kit the bleed in the overheads would cause problems with moving individual hits.
When you move the beats, you are simultaneously "moving" all the mics with them.
IOW...in the SD mixer, you have for example, the Snare top mic, bottom mic, and the OH mics. Moving a beat in time, doesn't change what the studio mics picked up. IOW....the bleed will stay accurate.
I've not found any kind of issues with bleed...and there's a reason you get such a HUGE library of samples. They cover all the nuances with real samples...so there's no fabricated shit going on.
That said...I tend to turn off a lot of the extra room mics and ambiance, and I like to trim back the bleed too, just to "dry up" the kit sound a bit more. They kinda give you the whole enchilada, with everything on it...but you have the option of using what works for your mix.