Nah, it's a nerf in the castle age and buff in the imperial age.+10F, -10G for Eagles is actually a buff more than a nerf. Eagles need directly nerf food cost without any compensation since the unit already is so cheap, it should be 30F, 50G or even 35F, 50G at least.
What makes eagles so powerful is how spammable they are in the early castle age, while allowing creation of villagers.
Increasing it's food cost by 50% is such a huge deal early on! And IMO would address the early castle age OP-ness of the eagle spam
Eagles are very much dealable in imperial age, so slightly buffing them for the imperial in fine IMO. Especially considering the central american civs don't have hussars as trash units (and cav in general)
Making it 35F and 50G would make these civs plummet. They will basically just turn into foot archer civs then 11