As to fillet and valet, they joined english before the contemporary french pronunciation, and are much closer to the middle-french.
My favorite is probably crepe, which Americans pronounce like an almost diphthong-y craype (or crape like grape I guess) when crep (like step) would do just fine and be closer to the original.
But as a native French and basically-native American speaker, I also couldn't really care less about it, or about things like Americans pronouncing the t in croissant, or French people being unable to say the.
I say it the American way when I speak English anyway because that's just how it is. :)
See also: Cairo, IL or Versailles, KY...
Fontainebleau State Park -> Fountain Blue State Park
These were two off the ones that really stood out from my travels.
But I also completely disagree, I don't think americans are attempting to pronounce croissant correctly for example, whereas brits will be much closer with no attempt at intentional mispronunciation, it just happens that brits are much closer on some and further on others, and vice versa re americans.
and I don't think there is any malice, in fact it became common among the british aspirational middle-class in the 70s to adopt french words in an attempt to appear cultured and upper, ironically now a clear marker of non-u.
Mon dieu Rodney!
If there were just French words pronounced in a French way and English words which came from French and are now pronounced in an English way that would be bad enough but in fact we have a whole spectrum of bastardisation.
It's not always that way though, consider 'niche': it's AmE that decided it's 'nitch'!
Fillet/valet are mis-pronounced because of mallet, pallet, etc. Renaissance? Nail, snail, tail, etc.
It really is that simple, we're just pronouncing them as if they were an English word.