Couldn't agree more. There isn't any relation at all. Ethics are after all the informal rules of behaviour, whereas quality of art is a somewhat subjective appraisal of ability in expression. The behaviour of an artist (and many of them are distinctly flakey, others extremely cunning) varies enormously, and since ethics are rarely imposed on artists, their own ethical codes vary along with their personalities and egos.
Be that as it may, this is far from the manner in which the Romans perceived artists. Along with actors, freedmen and musicians, artists were very much considered a package deal of immorality and slothfulness. The very notional that an individual is associated with actors and musicians would conjure up all sorts of imagery within the mind of the Roman elite - indeed Pliny the Elder describes theatres 'havens for perverts' - and by association with such types, they too embodied the traits assigned to actors. But the issue went further than this: an entourage of artists was also considered to be part of the iconography of what the Roman dubbed lincentia. This was fairly complex concept, but could be boiled down to meaning an excess of freedom, which existed both alongside and in isolation of the notion of servitude - vice was, after all, considered to be a form of cyrpto-slavery.
While Roman artists could well have been perfectly nice individuals in their own right, this does not escape the issues that the Roman aristocracy, at least in principle, viewed such types at a distance.