You don't get to be head of a Mafia Family by being a nice guy but compared to Michael how ruthless was Vito?

Vito is unable to order the death of his son-in-law though it is apparently obvious to a hysterical Connie that everyone blamed Carlo.

Later, Michael has no problem either ordering or countenancing the murder of a prostitute simply to get leverage over Geary. Could Vito have done that?

If Vito hadn't passed on when he did, how much longer would Carlo have gotten a pass? Plainly Vito knew Carlo would have to go. Would Michael have felt constrained from handling Carlo as long as Vito was alive just to spare Vito's feelings?

"When the snows fall and the white winds blow, the lone wolf dies but the pack survives."
Winter is Coming

Now this is the Law of the Jungle—as old and as true as the sky; And the wolf that shall keep it may prosper, but the wolf that shall break it must die.
As the creeper that girdles the tree-trunk, the Law runneth forward and back; For the strength of the Pack is the Wolf, and the strength of the Wolf is the Pack.