A few points: First, the HP gain you will obtain through Colossus is very marginal, and HPs are not all that useful anyways in terms of survivial in this game.
The amount you get depends on amount you have, so if you don’t level up HP per level and don’t have a character with good traits, then yes – increase will be marginal.
Second, more importantly, I simply do not understand why you would use a 2 hander on a unit not dedicated to DPS. No, I do not mean “offense is best defense.” I mean a non DPS character using a 2 hander will neither DPS well nor be survivable. It simply doesn’t make sense. Without Perfect Focus, you won’t swing a 2 hander more than once anyways in most cases. Even with Battle Flow, the swings won’t increase that much. And with Perfect Focus, you have no room to get into the Defense tree, because you need at least one Fatigue mitigating tier 2 Utility Perk. So explain to me what build are you trying to describe?
I don’t take Perfect Focus, because my two-handers would still be limited by their fatigue and restrict other uses (like shield splitting, for example). So I mainly pursue traits that help their fatigue, with survivability and damage being a bonus. It takes less points to do so. While they might not be DPS I don’t intend them to fill that role. They are my heavy hitters, shield crushers and tanks rolled into one. It works great, because I also have second line of billhooks and archers who fire from behind that safe line.