I think it depends on the alternative. Compared to no interruptions, this kind of behavior is annoying. But if the alternative would be pausing to pull out their phone and look to see why it just buzzed/dinged, the watch glance may be the lesser evil.
More important to me, in either case, is to tame the notifications no matter where they go. It is your choice what gets to the phone screen or the watch, and if you are pausing a conversation to glance at the watch and then it does not cause you to need to do something else urgently, this is a strong indication that you should have that notification turned off. Let it go to a low priority queue you can look at later when you have time, not something that buzzes or dings at you.
More important to me, in either case, is to tame the notifications no matter where they go. It is your choice what gets to the phone screen or the watch, and if you are pausing a conversation to glance at the watch and then it does not cause you to need to do something else urgently, this is a strong indication that you should have that notification turned off. Let it go to a low priority queue you can look at later when you have time, not something that buzzes or dings at you.