I’d change the CR rules. Too many times I believe a realistic encounter is ruined cause a rule lawyer complains it is too hard. The players should have to make appropriate knowledge checks to see if they can handle it but hiding behind a “that CR is too high”
I wouldn’t change CR. Instead, I’d make every monster actually conform properly to the rules set out. That monster is supposed to be CR 13? Does it check off all the beats down the list? Yes? Next monster then. Dragons are the only exception that I’ve never understood. It’s CR XX like these 20 other monsters that perfectly conform to the rules, yet the dragon is obviously CR XY. So why isn’t it that CR but instead this CR? It makes no sense. I get that they’re supposed to be “more” than a standard monster, but some times that AC is literally impossible to hit at higher levels. Which is even worse when you realize the amount of hp they have by comparison too. Personally, I’d add another clause to the ‘dragon type’, keep the AC normalized, and just ramp up the hit points like in 5e.