Currently you need to be more senior to get an internal RHS move to the 777 than you do to take a reasonably middle of seniority LHS on the 'bus out of Heathrow!
Progressive degradation of lifestyle on SH has led to many pilots taking lifestyle decisions and going part time whilst remaining RHS on a LH fleet.
So, yes, there are an awful lot of Captains who are much more junior than SFO's.