i dont think he did waste his life
he pursued his dream in creating a family.
his family was willing to fight for him till the very end and was a respected pirate. even the marines respected him.
out on the battefield in marineford, he guided his men to trying to save ace. they all trusted him and loyaly followed his orders
he was an awesome pirate!
i just want to mention that, if he had just sent his crew but stayed back to stay alive a bit longer, the out come would have been the same or worse. that would have been truly wasting his life because at least this way he died for something.
he died trying to save ace, sure he failed but its better than dying in bed morning one of your sons. so the true waste of his life would have been to not die the way he did. the only better out comes would have been to get away with ace or to die while ace actually got away. at least that's my opinion.
The question isn't how he acted during the war, by then he was a Old sick man - however he wasn't always old in sick, he could had done far more with his life then what he did.
He didn't know about Ace being Rogers son till at LEAST when Ace entered the NW, so for the years between Rogers death and Aces arrival he did NOTHING visible to change the world even though he had the power to.
He didn't know of Ace's existence, that is true, but he did know to the Will of D. What he was waiting for was someone to carry the Will of D. It just so happen that Ace came to his attention, as a Will of D carrier. He learned of his bloodline later on after Ace had joined.
You're acting like the only people who can change the world is those with D in their name... but obviously that's not true because people other then them have Conquerors Haki - WB had Conquerors Haki so what was stopping HIM from changing the world? in OPverse you inherit your Will, it stands to reason if you have Conquerors Haki you inherited your Will from a pretty strong/important person.
Also like, WB was not Rogers subordinate - there is NO evidence that Roger asked him to stop moving until someone with a D came around (not to mention Teach is ALSO a D and had been in WB's crew for years before Ace came) and even if he did - WB/Roger were rivals if WB didn't want whatever treasure there is at One Piece he could had done more to fight against the (increasingly evil) World Government.
While it's true that in theory, it doesn't need to be a person with the Will of D to change the world, but this is OP and it's clear that that's how it's been set. I mean Oda gave us the flash back with Roger for a reason. WB said to BB "Your not one of them" for a reason. The world gove is afraid of those with D in their name for a reason. Heck, Roger was going around the world, to find all those pyroglynth (sorry, can't remember what their called exactly), for a reason. We don't know what the D's are, nor what their purpose is. We don't know what the Void period is about either. What we do know is all the D's we've been shown have turned out to be great.
WB wasn't Roger's subordinate. No one said that. It's just, the Will of D is something so great, it's kinda like Roger's dream. Like Rayleigh said, Roger could hardly care about the title of PK. WB had achieved his own dream of creating a great family. Roger is a man he had huge respect for, much like Shanks, Garp and Sengoku respected WB. There's no other reason for him to help push forward the Will of D; much like there was no reason for him to aid and protect Luffy to protect the will, or there wasn't really a reason for Garp to listen to a pirate and raise his son.