There's nothing wrong with it, it's the nature of audio. You can only time stretch so far and like Peter said it also depends on the instrument and frequency range.
Everything in life has tradeoffs. The tradeoff here is the awesome quality of the sound of the RT's but limited tempo's for each one. The only answer is to create more tracks at more tempos and that is happening. BUT, another tradeoff: Storage. A complete library of RT's at all tempo's will probably fill up a terabyte hard drive but they're cheap enough it's worth it. At that point there will have to be some kind of filter system you can program so you're not looking at every RT you have on your system every time you want to use one.

Bob

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