dude thats how some of the old games are turn on xp share
no they litterly arent. EXP share thins out the EXP shared between pokemon and turning it off puts it all on one pokemon so you should earn more. EXP share was introduced in gen 5 and only worked between one other pokemon.
the remakes of gen 2 and 3 had it between the entire party. turning it off would make the one pokemon you battle with gain more exp so you could grind easier for ONE specific pokemon.