There's many grey area's within comparisons but a decent CL run doesn't mean anything in the grand scheme of things, neither does a bad one. Fergie went out in the group stages a couple of times and also won it.
I agree that Ten Hag is a risk, especially when you also consider Barcelona, Madrid, Chelsea, Juventus, Bayern, Inter, Tottenham, Dortmund, PSG, Roma and even Newcastle have all changed managers in the last 12 months and Ten Hag wasn't even considered by any of those clubs.
Surely "the next big thing" would have been heavily courted by a few of those big names?