I don't think anyone is disputing that England has a huge production potential.
That has never been the issue afaik. The issue is commerce and an OP France imo.
If the French AI were somewhat capable they could easily crush England (AI or Player).
Knights vs Crossbowmen = dead Crossbowmen

Not to mention the high probability of France having Teutonic Knights or Knights Templar.
I've tried a 'cheating' approach too (preplay as France).
I sorta ruined France (war with everybody, bad economy, backwards in techs etc.) and built Calais and Caen very early including complete priority on those two cities.
But once the flip came something odd happened.. although France was nowhere near Chivalry (not even plate armor) they had Knights two turns later -.-
They must have mad peace and traded it in from someone..
I sometimes get the feeling that the AI might even be gifting techs to eachother
The AI does do things like that, I've had Byzantium, Rome, Germany, France all gift me techs at one time or the other, sometimes even fairly important ones (like Civil Service, Replaceable Parts or Drama)
and btw just thought of another thing
in normal RFC you couldn't trade a follow up tech in the same turn, now if your trading partner is nice enough and has the techs you could go from early medieval to industrial age in 1 turn.
it's nice enough when you get to jump ahead but I think that that might also be something to think about (it sure speeds up the overall tech rate if the AI trades smart)