Stop lying when these things are way too easy to check. Cassidy's number 1 choice against McDavid when he had last change this year was Chara (who had 13 minutes and 43 seconds against McDavid) and McAvoy (who had 11 minutes and 34 seconds), compared to the 1 minutes and 54 seconds Carlo got. Carlo got more time against McDavid when they visited Edmonton but still less than Chara/McAvoy. When Cassidy had the last change vs Edmonton, he primarily matched him against the Oilers 3rd and 4th lines consisting of guys like Ryan Strome and Puljuarvi.
So, if your case is that Carlo is worthy of going top 10, because Cassidy matches him against McDavid, your entire argument is flawed. Because, Cassidy seems to avoid doing that.
Edmonton Oilers @ Boston Bruins, 2018-10-11
Boston Bruins @ Edmonton Oilers, 2018-10-18
Since you are pushing this point, maybe you have it wrong and it was last year. Except, nope. Last year at home Cassidy matched Chara and McAvoy against McDavid at home. The same applied on the road.
Edmonton Oilers @ Boston Bruins, 2017-11-26
Boston Bruins @ Edmonton Oilers, 2018-02-20
I'll even go back to Claude Julien. At home, McDavid was primarily matched by Chara and McQuaid, with Carlo getting 3 minutes and 30 seconds. He was 2nd behind Chara for the road game.
Boston Bruins @ Edmonton Oilers, 2017-03-16
Edmonton Oilers @ Boston Bruins, 2017-01-05
It's pretty evident, that over the last 3 years since Carlo entered the league, he has never been the preferred shut-down guy against McDavid. That responsibility has always fallen to Zdeno Chara, who is usually with Charlie McAvoy. This lines up with his QOC TOI% which shows Chara and his partner always get the toughest shut-down minutes. Usually with Bergeron's line doing heavy lifting too.