I'm not arguing that Hunter should or shouldn't be in the Hall of Fame. And I'm also not arguing that situational pitching doesn't happen.
Hunter's ERA is 3.26. His adjusted ERA+ is 105. Those aren't great numbers. If you want to argue that those aren't true reflections of his skill because he pitched to the score, you'll need to show some actual evidence.
Other pitchers pitched in the same era as him, got lots of run support, pitched a ton of innings, and were still able to keep their ERA lower. Jim Palmer, for example. He pitched more innings in the same era, got exactly the same amount of run support (4.4 runs per game), averaged more innings per start, threw more complete games and more shutouts. Yet his ERA is 2.86 and his ERA+ is 126.
By your logic, his numbers should have taken a hit because he was eating innings and pitching to contact. But they don't.