If that was true , why do teams send 11 men onto the field at the start. (dunno) (dunno) It annoys me when I hear this excuse, yes teams tend to get players into a more defensive system , but having 1 player extra that should give you the edge, against Barnsley it works the other way round. Colchester were the better team until we lost Reid.
I think sometimes the tactic/formation change by affected team just happens to work therefore making it look like it is harder to play against 10 men. Also, maybe the remaining players step up their game (begging the question why weren't they doing this in the first place). Football is such a funny old game isn't it.