Mangudai are very weak even with upgrades, please give them more HP earlhy game.
In my opinion, if you want to buff them it should be in the late game, they already harass quite well in early, if you buff them in early I don’t know how are you going to stop them killing villagers.
I play mongols as my main, i don’t think it’s a good idea to buff mangudai. It’s a very good unit as it is, it’s extremely weak against archers in the beginning but you can upgrade their armor quite fast and use them to harass vilagers. Or horseman mangudai combo is also strong.