That's also not true.
Jinbei is not of Luffy's generation. Plenty of people fighting with Luffy won't be Luffy's generation. RA commanders aren't of Luffy's generation.
Dragon will die to Imu, after Luffy takes over the fight for him and after they have the father/son fighting moment. But neither Garp & Dragon are dying before they face off against Imu. Imu vs Monkey D. Trio is the clear build up for the final fight.
Okay I mean that might be cool but it's totally your very specific headcanon.
I'm just saying the guy leading the charge of the revolutionary army in the final battle will have to be someone young like Sabo.
Having Dragon do that will be awkward because he's Luffy's dad.
It's one thing to have Jinbei as a crew member. It's another thing to have your main ally be Rayleigh instead of Law, for example.