OK my two cents:
First, I think the weight of the evidence suggests that the Brits are not in the thick area of the bell curve but are in fact UP. I usually play the Brits and although they are competitive, other civs simply outproduce them early and late. I usually outproduce opposing Brits, so I'm pretty good at my eco, but seemingly everytime I beat a Japanese or Dutch player of equal skill he has out produced me. Second, as has been exhaustively discussed, the British NEED their longbows because everyone needs skirmishers, and longbows have "issues." Third, the British musketeer is O.K. and that is all, better than some and worse than others. Fourth, they don't have a hand infantry option, and so their middle of the road musketeer plays "halbedier." (so, unlike the dutch you is to protect the longbow from 4 legged things? - yes, the trusty but average musketeer). Last, and perhaps most important, the hard stats are that the British don't do well.
It seems to me that equal against equal the Brits have at least a slight disadvantage that is leading to their dismal statistics.
I have two changes that I think may make them more middle of the road early/mid and late game, but not OP.
1. Let them build X more houses (perhaps 10 more). This gives them 10 more vills at the cost of 10 houses. (this gives the British player the option of significantly increasing their eco early/mid game but doesn't change their late game eco which is respectable.
2. When the Yeomen card is played longbows cost 40 gold instead of 40 wood. (since gold is less expensive than wood, longbows become cheaper, and also wood must be acquired mid/late game away from your base - if the British is on the defensive he loses the long bow option (and their is a 100% chance he will be up against skirmishers).
After saying all of the above, I know a Lt. Colonel who plays the Brits all the time, indicating she doesn't think they are UP, but then she is a Lt. Colonel and could play as "Mr. Bunny" and still beat me.
My point is, I accept that I may be wrong about them being UP.
What do you think?