I didn't mean to imply that managers can single-handedly fire whomever they want. But empirically good managers can get bad engineers fired, but good engineers can't get bad managers fired nearly as easily (if at all).

The managers werent the ones who flipped the switch with HR to start the firing process and provided the evidence to make the decision?

Not always. Managers sometimes like the people on their teams, and don't want to fire them. That's when someone else notices the team needs shaking up, or overhears conversations that are unsettling, etc. Also step-over meetings, too: that's when a manager's manager (or higher-up) will have a meeting with someone the manager is managing....good orgs have all these types of playbooks.

"Managers sometimes like the people on their teams, and don't want to fire them."

I remember early in my career meeting a very senior and experienced manager from another company on the same project who said he intentionally didn't become too friendly with people in case he had to sack them - which I thought must be a miserable way to live. NB I have sacked people for poor performance and laid off people I considered friends (and who are still friends).

I haven't heard of a modern tech company of any size that allows a team lead / direct manager of ICs to unilaterally fire a report without some decent amount of process and involvement from others.