I don't really think that the async or blockingness is the leak, but that the time taken to process is not defined in either case, and you can leak failure crit

I don't really think that the async or blockingness is the leak, but that the time taken to process is not defined in either case, and you can leak failure criteria either way by not holding to that same time. People can build to your async process finishing in 10ms, but if suddenly it takes 1s, it fails