I have a project of similar scope, a native mobile app I have been working on for four months.
I get the same kind of snarky comments when I talk about it. Amazing how people who know nothing about the project think they know better than me about its quality or maintainability.
I doubt it's anything in particular that we are doing, I suspect it is rather a lack of trying and experience with the ones who are claiming agentic development does not work.
I have not once seen a believable story where for example the project broke down after 200k LOC, or after going live.
It is always inane stuff like in the OP, like the agent supposedly generated only tests and no code, sure.
Most of the ones I have seen were "I generated some code and did not like the output". No attempts of iterating and refactoring.
I believe they simply did not yet try our way of working.