There is something that has always bothered me about how Roger's life ended. Being the Pirate King, you would expect him to be off-the-scale strong, so how was he captured by marines? It would have had to be a really strong marine head, but anyone strong enough to capture Roger would really have to be the strongest in the world and I find it hard to believe that such a powerful marine could stay righteous for long. After all, power tends to corrupt, so if a marine had taken Roger down, I'd assume that by now this marine would be a pirate or something much more profitable.
Rather, it seems more likely to me that Roger was taken down after being bloodied in a fight with another powerful pirate (say, Whitebeard). In such a weak condition, it would be easy for a powerful marine like Aokiji to capture him. However, this gives me questions about why Roger did not escape when being walked down the streets of Loguetown by a few weak marines. Even if the shackles on his arms were made of steel, the Pirate King should not have any problem breaking them off with his strength.
Had he given up on life because he already had as much as he could? Or were the shackles made of that mineral that possess the ocean's energy–in which case Roger would be a Devil Fruit user--so he couldn't escape even if he wanted to? Only these two explanations really make sense to me. Why didn't his crew, which undoubtedly must have been incredibly powerful, do anything anyway?
It further puzzles me how two spears could end Roger's life. Come on, Luffy took countless stabs from Don Krieg and two stabs from two measly marines killed Roger? That's a huge inconsistency there.
The same applies to how Shanks lost his arm. Luffy had no trouble defeating the Sea King after he left Cocoyashi, but Shanks couldn't take care of the Sea King without losing his arm when he's an infamous pirate respected by Mihawk and Whitebeard? I understand that it is a pivotal moment in the story and I love Shanks because of it, but I can't help but feel it is terribly inconsistent.