That has been my experience, yes. You need one full-time manager, one full-time on-call/pager duty (usually a rotation), and then 4-6 people doing feature development, bug fixes, and operational stuff (e.g. applying security patches, tuning alarms, upgrading instance types, tuning auto-scaling groups, etc. etc.).

Maybe you can do it a bit cheaper, e.g. with 4-6 people, but my point is that there's an on-going cost of ownership that any custom-built solution tends to incur.

Amortizing that cost over many customers is essentially the entire business model of AWS :)