And yet they're still smaller than the largest extant real world rodent, the capybara. I could make another comparison and say that the giant rats are about the size of a goat - which implies something completely different about their combat ability.
Comparing them, based solely on weight, to a dog specifically bred and trained for combat (or to a goat) is a poor comparison because it implies something grossly misleading about the rats' build and the threat they pose. They might both be 50 lbs. but giant rats have the skeletal and muscular build of rats, not war dogs (or goats). It's a rather large difference:
vs.
The giant rat is certainly "icky" but it doesn't have the body shape to be a dangerous combatant like the war dog. Any disease possibly carried by the rat could be extremely deadly, but that's an entirely different issue.
I'll admit that I'm amused to read that "players consistently feel that their characters don’t have enough hit points" and WotC's reaction is basically say "too bad...though I guess we can give the wizard a bump." LOL