The comment that a band is "good at what it does" is a polite attempt to acknowledge the talents of a group outside of one's wheelhouse. But the phrase tends to come off as a dismissive, backhanded compliment, the type of statement a person makes to avoid actually forming an opinion. The underlying element of snark comes from the dynamic between good and cool. Any musician, given enough practice, can be "good"; this is a prerequisite to get the most basic gig. Fewer musicians have reached the vague pinnacle of "cool."