I've been maining Stryker with him for like 6 months, I don't really mind having less health as long as I'm getting clocks up. Imo rewinding/breaking out of a combo is effectively the same as gaining the amount of life you would have lost in the combo, so Geras pretty often has an effective total health of like 1300 or more per round.
As for Mavado's utility otherwise, after labbing it more I think he might be good for Geras after all! He helps build clocks in combos well, pretty simple series of just B12 xx clock while calling Mavado ground bounce lets you keep the juggle going into S12 ex freeze, etc. He converts weird hits into damage and oki, like if tornado hits anywhere you can turn it into a ground bounce into inevitable etc. More importantly his move that slams you together with the opp gives big meaty plus frames on hit and good plus frames on block, and his mine creates an in escapable launcher when placed just before F12 xx command grab.
I usually pick assists for safety and neutral, hence Stryker but also I played Kano before that. Mavado can't make tornado safe on block, so although it's nice to get combos out of, it's still a big risk in many matchups. But I can see this being good on a Geras playstyle that's more committal. I'm gonna give him a good try for a while, we'll see.