Many factors that can change over the life of a pension make it a difficult comparison, IMO. Will the FS scheme still be open when you retire? I’m 29 and on a FS scheme, but I don’t expect to still be on it forever, chances are it will be closed before then (it’s already closed to new members)
I’d estimate how much you expect to be on when you retire on should you stay in the scheme ( in today’s money) then work out the size of pension pot to guarantee that income via annuity? It’s probably a pretty eye watering sum.
Also worth considering, could you reasonably stay at this company for the rest of your career without getting bored?