I have the same issue. Wifi keeps on dropping especially while streaming videos. This is really annoying and the troubleshooting steps you provide is not helping. I am not sure if this is a bug from the recent iOS update or some kind of hardware issue that this needs to be checked/verified by Apple Tech support.
I keep on calling Apple Help Desk for this issue but the line was busy.
FYI - its not with the router coz mine, its just besides me.