I highly doubt that would be successful - the last time I checked, no FH involves FU units. You'd need two early monuments to get enough favour for Greatest of Fifty upgrade (which is essential to making Spearmen counter Cavalry effectively) let alone any other mythical upgrade. You spend 1300 Food, 1000 Gold and 40 Favour just to make your Spearmen able to counter his Jarls...why? Also, he'll be making many more Jarls whilst you're advancing to the Mythic Age and once you've spent all of your gold on getting to the Mythic Age and making some Barracks and Spearmen, you're not going to have much left for a Migdol at a second gold mine either.
If you were going to FM (and turtle) in this situation, it would be for Son of Osiris + Mummies + Catapults in Rocs I would think, not Horus Spearmen. But I still doubt an FM is a good strategy in the first place to counter a Bragi FH. :/
Take my love, take my land, take me where I cannot stand.
I don't care, I'm still free, you can't take the sky from me.
Take me out to the black, tell them I ain't comin' back.
Burn the land and boil the sea, you can't take the sky from me.
There's no place I can be, since I found Serenity.
But you can't take the sky from me...