If 'high fantasy' is to have any meaning as the name of a genre, then it must include both good and bad works. (Just like there are good space operas and bad space operas, good Regency romances and bad Regency romances, etc.)

I was first taught that 'high fantasy' meant that the setting was unrelated to the real world, which seems to be closer to Lloyd Alexander's meaning when he coined the term (though I haven't read the article) than most definitions one sees these days. For instance, Wikipedia and TVTropes contradict each other on what the distinction is.

The use of the word 'high' may be to blame, since people are apt to interpret 'high' as meaning 'good' or 'high-status'* and try to redefine the term such that "things I like are high fantasy, things I don't like are 'low'". And then we end up with a million different definitions of what these things are (up to and including "I know it when I see it") and the terms become useless.

This is probably why fantasy subgenres are given more literal names (secondary-world fantasy vs. urban fantasy vs. portal fantasy) in discourse where you want to make sure people actually understand what you're talking about. Because the definitions of the older terms are so eroded, there's usually a better way to say what you mean by "low fantasy" in a particular case (e.g. if it's "low-magic secondary-world fantasy" or "gritty portal fantasy", you can just say that).

*Cf. the extremely common misconception that "High German" vs. "Low German" is a distinction of social class, rather than geography (literally highland and lowland).