My opinion is that if you can taste the grinder in your espresso shots, it might be a good time to thoroughly clean your grinder...

People do have very strong ideas about grinders tasting different and they love to place them in a linear scale. Reminds me of the scene in Dead Poets Society where poetry was explained by mapping poets into two dimensional scale. As you can see, poetry is more involved than coffee because it needs two dimensions.

From a statistical point of view, any sensible formalisation of "grinder X is better than Y, and on par with Z" is utterly impossible to establish. Espresso tastes like coffee (and water), because that's what it is made of. Espresso extraction is very complicated and has an immense effect on how the taste is reproduced in the cup. I don't deny that the grinder would not have an important role here, but talks about one quality grinder tasting "slightly better" or "on par" with some other quality grinder are, well, a bit silly, I think.
AFAIK the only way the grinder directly affects taste is that it heats beans and can create burnt flavours. It also indirectly affects extraction by producing different amounts of fines and different distribution of particle sizes in general, and by distributing grounds in basket differently (which can be rectified with grooming techniques). There probably are other factors also. Taken together, it is hard to see how such a complicated dependence between grinders and their (subjective) "tastes" could be explained on a linear scale.