Maybe I'm too optimistic, but given appropriate skills and references (not just for writing but also reviewing) and intelligent use of subagents for isolated reviews and checks, you can lengthen the leash a bit.

But you still need to properly review plans and PRs to keep a good mental model of the codebase. This effectively limits the number of tasks being done in parallel to maybe 2-3. Though you'll be mentally exhausted and probably start to make mistakes or take shortcuts in reviews yourself.