I have character deaths. I have close calls.
I think you overlooked the parts of my comment that I considered necessary to the point, I probably should've bolded them or expanded on them
1. "Appropriate-CR" monsters are a pushover for high level characters. The Pit Fiends, generals of hell, have +14 to hit; one character had 35 AC, the other was in the high-20s. Even if they were hit, they had lots of ways to negate or avoid those hits. The two characters, between them, could easily weather and restore themselves from anything the pit fiend or devils could actually do to them. Those two characters probably could've handled an Ancient Blue without any real chance of danger. TWO characters, not even a party of four :')