Well then, you are being selective if you compare Waqar (who is probably the faster wicket taker in history with 300+ wickets) to Warne and then comparing Garner to Warne. Warne and Garner have a difference of 7 balls per wicket which is about the difference between Waqar and Garner. And again, it should be reiterated that Warne bowled at times when naturally wicket-taking would be harder to do. That's why the difference between them is negligible. Having a spinner who takes wickets almost as cheaply and as fast as ATG bowlers is wonderful.
Gibbs, however, is not such a spinner. It's not that Gibbs is a bad spinner or anything, he is among the very good ones. However, in general, spinners have an inferior output to that of pacers bar a very select group - namely, Warne, Murali, O'Reilly and probably Grimmett.
As to your other question; I'd say yes - the pacers of Warne's era were superior. Both in number and quality, I'd argue. I am not sure about the ICC ratings, I don't consider them much of a guide really.