There is M1 and there is M2, and then there's Director. There's no level 6+ on the management track. I'll disagree with this statement by saying that I think the step function in skills between managing people and managing people who manage people is huge. There are larger gaps between M1 -> M2 -> D than IC6 -> IC7 -> IC8...

but, I think the answer depends. If you are a really strong individual contributor, I presume getting an IC promotion is easier. If you are just decent, getting an IC7+ promotion seems incredibly challenging because IC7 requires an very high level of competence. If you are just decent as a manager, you can get luckier.