The METR result is the part people should sit with. Experienced developers were 19% slower on their own repositories and still believed they were about 20% faster, which means the feeling of speed is no longer evidence.
"Pick one pain point, execute well" carries a lot of your argument. The solo or small team mode fits bounded scope, greenfield code, little compliance and domain knowledge already in hand. Once the blast radius is shared or regulators want an audit trail, the work that is not typing comes back.
The GitClear numbers on duplication read like the cost of every engineer working from private context. A team owned AGENTS.md, reviewed like code, is a cheap fix for that.
Your closing question is a good one for clients as well: if the strongest engineer left tomorrow, could the rest of the team explain what the agents have been writing? For outside builds we treat that handover as part of done.