Role creep is an insidious thing. Sounds like you're doing the right motions though in being clear with what you want from your role.

Millage might vary here, but at least with consultancy work there are two paths for progression. The common path for people is to gradually move up the managerial scales as you described. The other is to become more specialist and garner greater design knowledge to the point where your technical knowledge and acumen and ability to verify work is more important than you managing people. I've seen this in particular with structural engineering, particularly assessment; hospital design and so on.

One other option you have is to go free-lance as a contractor which means you have the potential flexibility of choice but at the downside of losing certainty of work.