Right, but if PMTUD is broken, basically large transfers to clients with low MTU don't and never will work, and there's not much you can do about it. It's not

Right, but if PMTUD is broken, basically large transfers to clients with low MTU don't and never will work, and there's not much you can do about it. It's not like it's an "unreliable connection" which can be worked around with error correction. It's a "broken connection", which needs to be fixed.