I'm only an Emperor level player, but the current incarnation of Washington seems extremely strong, mostly due to the effects of the Pioneer Fort. The +50% Surplus food effect is almost as strong as an Aqueduct (effectively +67% Surplus food due to 1/0.6 from 40% of the food being stored) on its own, but the true issue is that the effect *multiplies* with the effect of the aqueduct for effectively +150% Surplus food, meaning 2.5x growth speed. In addition to this, the Pioneer fort's "secondary effect" of +5 Defense can be fairly useful in that it gives you more breathing room on defense, allowing you to dedicate more resources to building the city up fast and powerful.

Pioneer Forts are available extremely early, even faster than Aqueducts, with Masonry being a tier 2 tech (one which also unlocks a semi-common luxury resource), and are as cheap as the other low level growth buildings (Granary, Waterwheel). Getting both P-Forts and Aqueducts up in cities requires a decent amount of production, but the 2.5x growth speed bonus is a little bit outrageous even for that, especially that early in the game. Lighthouse+PF+Aqueduct is especially disgusting with the current 2/0/1 coast tiles (which produce effectively 3*2.5=7.5 surplus food extra for each worked beyond the stagnation value), and its an easy way for anyone to see what I'm talking about.

In addition, Washington's other traits are fairly good. +1 sight is especially good for getting good starts, since it helps so much snagging goody huts. -50% Purchase is quite a useful bonus too, and Minutemen are perfectly placed to take advantage of the massive cities you can grow with the Pioneer Forts and Aqueducts together.

I think that the best solution to this would actually be to retool the Aqueduct to become a +% Food Surplus bonus, so it no longer effectively multiplies (only adds) with the P-Fort (and to much lesser extent of horror, Landed Elite). The bonus itself on the P-Fort could also be toned down a bit, or the Hammer price or even tech tree location of the P-Fort could be changed. As it is though, Washington's unconditional food bonus makes him seem to be an overdominating contender for a lot of games. (Montezuma's UB is also very strong, but at least it requires you build on a river or a lake, which can be tricky for various reasons at times).

I think the Pioneer Fort is just alright and really welcome for Washington.

There's a few limiting factors:


The value of food is capped by available happiness. I spend most of my time right at the happiness cap, so growth boosters aren't quite as useful as they might be otherwise.
The Pioneer Fort only helps cities reach their potential faster, whereas the Chinampa increases that potential by raising the base food available to the city. In addition to the flat modifier, Chinampas turn lakes into powerhouse tiles.
Washington's UU is a Musketman replacement. Musketmen and Sipahi are arguably some of the weakest units in the game, so the value of it isn't tremendously high. In contrast Jaguars are available very early, and their healing promotion carries over when upgraded to Swords and Longswords. The Aztec trait is also very useful for both policies and border expansion.

Some of these comparisons are lopsided towards one leader or the other, but overall I'd say the Aztecs and Washington are probably equal in value, which is the goal. Washington was rated second-tier on the 5 Favorite Leaders poll (http://forums.civfanatics.com/showthread.php?t=413025) so I think his buff is justified. :)

One way of looking at the cumulative Leader changes is that almost every civ could arguably be called borderline OP. This makes them both roughly equal and a lot of fun. I had zero interest in America or Germany before their buffs. I do no better with them than with my traditional favorites, but I can't stop playing with them.

That's basically the goal of balance. Make everything feel overpowered! If it all feels that way then it's both balanced and fun. That's what I did with my Balin's Tomb mod for WCIII years ago... people said all their heroes felt overpowered, yet their scores were equal and they were struggling against the challenging boss fights, so in reality it was very balanced.

Watching some of my games, the reason the Washington AI does so well is his bonuses are very AI-friendly. He doesn't have fancy unique units or complicated abilities like Rome. Washington can just build the same way AIs always do and be great. Score is also heavily determined by population and territory, both of which he has bonuses in.