
I think it very much depends on the size of the dogs, and how the walks are structured.
I can happily walk four Elkhounds, and have occasionally walked five, but then the four are now all over 3 years old, and none prone to suddenly drag me off after a cat or something.
I walked my friends Dobermans sometimes, and would not feel happy walking more than one as a puppy/Junior, but have walked two well trained adults, and been able to control them when they have spotted a cat, when they were mature, but adults in their prime. I could manage two oldies with a baby puppy also.
So for me I feel happy that I can control on lead two adult dobes, or four adult Elkhounds/Springers, 3 Golden Retrievers, 2 Labradors, One Great Dane/Rottweiler.
It isn't just the weight, but the amount of street room the dogs take up.
I wouldn't feel happy letting more than one (possibly two really reliable) dog/s off lead that didn't belong to me, so that I can watch it carefully, and only if I know it so well, that it has the sort of respect for me that it will do as I say.