You’re not missing a setting; this is expected today. default isn’t a routing fallback: omitting --pool-name only names that pool default. A trigger with no pool= matches on repo= alone, so on a monorepo every pool sharing that repo (default, ios, both -dev) is equally eligible and whichever worker is free claims it. Routing Rules won’t help either, since they only map repos to environments, not pools.
The only deterministic lever today is naming the pool on the trigger (pool=default for the general fleet), or keeping the -dev workers offline when you’re not iterating on them so they drop out of the candidate set.
The real fix, untargeted work landing on a sensible default without typing pool= (ideally inferred from the task), is exactly the gap in the thread you linked, so best to keep it consolidated there.