It may be that critting 10% to 15% of the time is part of the "balanced in its unbalancedness" of the 5e classes. The champion might need that to contribute equally with his companions. As for critting Orcus: he's a champion! While others are spending their time focusing on flashy magic or hugging trees, he focuses on being the toughest SOB who can hit in the most devastating places. For Orcus, it just means his mosquito bites are a little bigger.I favor the interpretation that this equals the old improved crit from 3rd Ed. I mean should a third level champion fighting Orcus have a 10% chance on all his attacks to auto crit? No, you should still have to hit or roll a 20.
I'm trying to like 5th ed. but this lack of clarity on some of the most basic rules is starting to irk me. I don't remember this vagueness in 3rd edition.