For your question I could imagine it is lol. I had team of six but I'm sure it would have been just as easy to beat the game only using the starter since he'd be way higher leveled than everyone from fighting every battle. Overall the game is way too easy. And yeah the exp share gives the Pokemon fighting 100% of the exp and everyone else in your party gets exactly half of what the guy fighting gets. Say its 100 exp. Your Pokemon battling gets all 100 while everyone else receives 50 pts each.