The question with Starring is, when is it considered the same thing as Guest Star or Show Cast, and when isn't it?
For instance, no matter how often it was used on Twilight Zone, nobody thought that Buddy Ebsen or Cloris Leachman or Joe Mantell "starred on" The Twilight Zone. That's even less so today. Ask anyone and 99 out of 100 people will say that Joe Mantell wasn't a star of the Twilight Zone. And that the only person who starred on the show was Rod Serling. (who, ironically, was uncredited in his "show cast" role as narrator).
So if most people come along here and sees Joe Mantell listed as "Starring" in "Nervous Man in a Four Dollar Room," if they bother at all then they're going to change him to a guest star. Because he's literally a star who guested.
Ditto with examples like Millennium or House. If Peter Jacobson appeared in every episode of season 5 of House, what purpose does listing him as Starring (which I believe he was credited as) or Regular serve rather than listing him as Show Cast for episodes in that season?
So IMO, the question is what does TVMaze want to do? Go for the literal truth, which varies by era and country? Or provide broad caetgories? Listing the people above as Starring may literally be the truth as far as how they're credited onscreen. But... if it causes more edits (which cause more errors), and goes against "conventional wisdom", is the overall benefit greater or worse?