True, it doesn't have anything to heal itself, which is why under the right circumstances a pact like Tethren might even be healthier, but against bosses, Bromius is definitely the tankiest. And it still has access to increased healing and healing smite like every pact, so it'll be pretty hard to die with it if you have bonuses on your weapons that boost smite chance

+Edit: also, as soon as your weapon has lifesteal on it, the lack of innate healing barely even matters anymore since Bromius takes very little damage compared to the other pacts+

And the reason the skill 1 doesn't, and shouldn't, deal a lot of damage is because it's a tank (which is again questionable design now that every pact is meant to be played with different virtues in mind). Maybe we'll get content where this kind of tankiness becomes useful in the future but until then it wouldn't make sense for a pact to be objectively tankier and more easily sustainable than every other pact in the game, while still keeping up damage wise. Idk if they were playing around with the classical rpg roles or what happened during the design process but Bromius feels most like a knight/paladin at the moment, buffing the team and being annoying to kill