[patrec]

Is this based on conjecture or personal experience from working on multi-dev projects with both hygienic and unhygienic macro systems?

I lack such comparative experience but my guess would be that if your org's development approach is such that inexperienced people churn out dodgy macros without more expert review you are screwed and having a hygienic macro system will not save you. I'm very sceptical hygienic macros are at all comparable in utility to what a type system provides for multi-dev projects of any size. These benefits of types at scale are fairly massive and apply to basically any code. In contrast macros should make up a tiny amount (much less than 5% certainly) of code in a non-trivial application code base which means careful review is not a big overhead (and in my experience competent programmers do not introduce a lot of hygiene problems). So to be equivalent, in those instances where you do get a benefit from hygiene, that benefit would need to be absolutely massive compared to the average benefit you get of types.