So what's the overriding factor, experience or seniority?
Well we definitely mastered the way we calculate Seniority but how do you measure Experience? Someone on the big thread in R&N said 9000 time 1 hour doesn't mean 9000 hours flight experience?
So what about those Captains and FOs with zero hours on the 380 and 787?
Changing platform from LHS to LHS and from Heavy to Heavy shouldn't be a big deal also if you change the aircraft philosophy.
But upgrading a RHS medium platform to heavy LHS new philosophy platform can be challenging. Not impossible but you definitely introduce more variable with more chances of failure.