Wessex, I believe that +Williamson did not exit with a large chunk of the English speaking world because he has never stood up and said "Follow Me!". I've spoke to a few SSPX priests about a year ago now. Some of the comments they made about the Resistance was "They don't even have a Bishop. For any religious order to vialble, they must have a Bishop".
I think things have settled a bit, but had +Williamson stood up strong, I'm thinking that perhaps the number of resistance priests would be larger.
Just my 2 cents.