France's ability ends with Steam Power in part because they gain access to the Foreign Legion around that time, which is a vehry strong aggressive unit. The Aztecs have nothing like that. (Though a Jaguar promoted through the ages can make for a darn scary Infantry unit.) There's no reason for the Aztec's ability to come to an superficial end. None.
And while I agree that England is certainly not one of the stronger Civs currently (look up my topic: "England...sucks"), that's largely because of the way naval warfare is implemented in the current game. I'm willing to bet that under the new naval rules, England's super fast melee ships and embarked units will look pretty darn scary to coastal cities. They may take a look at England's UA with the Expansion, but the fact that they haven't already patched England when other UAs got a buff makes me conclude they won't do so with the new release when England's already presupposed to get stronger
That makes ZERO sense, considering one has nothing to do with the other.
If you want to use that argument, then look at the Aztec UB. 15% growth in the late game as it is now when you get fertilizers and all the food/farming bonuses. That is probably the most imbalanced UB out there if you have the right terrain for it.
What doesn't make sense, for me at least, is a civ getting sacrifice bonuses if they are in the Rationalism or Democracy branch.
But even if we go with Autocracy and the whole Hitleresque campaign in our game, I guess human sacrifice could be relevant for that civilization. I just don't know kills lead to more social policies, since that is what obtaining culture is all about in this game.
I would change the bonus to add Faith, and then add toward research after reaching the Industrial Era. At least get a science bonus for killing off more advanced tech.
And back to England, my only point is that another civ can rush the Great Lighthouse, and if you miss it by a turn, you don't have a UA in your game any longer, since that wonder gives 2+ movement to sea units and it is darn early in the game. Now if you hit it with England, you are pretty much going for an all navy game, but what if it is a Panagea or you can't exploit it enough because of the map? On the other hand, you hit that wonder on an Archipelago map as England and it is basically GG. BAD game play.