> A senior with Max plan beats three junior hires (very rough estimate).

If you have seniors doing the job of juniors, you will soon have no seniors either. If you have a senior doing the job of 3 juniors (which is different than doing 3x kind of tasks), then your senior will burn out and leave as well.

Also, as senior I enjoy working with juniors because I like to teach and share (with seniors that’s also possible but happens way less often). Working in a team of full senior+ engineers is not fun (in regular companies I mean): too much ego, politics, bias… no open to change