No one expects SubLabXL to be a proper sampler like Kontakt, but sound quality could be greatly improved if the sampler had a key split range and supported multiple samples allowing at least 1 sample per octave. That way the artifacts and timing issues of simply playing a single sample with a different playrate over the entire range could be avoided.
Ideally samples would be automatically mapped if the folder contains variations like filenameC1, filenameC2 etc.