Keep evading and taking potshots until he begins charging fire into his fist. If he's about to punch the ground, get away. If he's about to lunge at you, stand still and block it. Then do the QTE to deal massive damage.
Basically, get him down to 150%. Then I hope you're good with Blade Mode. If you are... boom. Lots of damage, and nanopastes.
Congrats man! One thing I personally also find to work is to not equip Nanopaste during the MG:E and early Armstrong fights as most of those can be done in a minute if you don't mess up, that way you'll be fully nanopasted during the final boss : ) Good luck on Revengeance!
I had this same issue on revengence mode. What I did was the other battles with Armstrong and metal gear I unequiped nano past and beat those phases without it. Then when I got to the final battle I equipped my paste and destroyed him.
I should add though that I also had the white armor which allowed me to have 10 pastes. Funny thing though is when I got back to the final battle with those pastes I never even had to use one. All my parries landed and I was able to evade all of his attacks.
I think this happened because I took an hour break from the game and did the whole level over. Having the 10 pastes in the end took away the stress of dying in one hit which madeir easier to relax and time my attacks and parries.