So, were the other 5 friends before Twilight showed up?
I don't see how they would be.
Rarity and AJ are opposites who clash before getting over it in an episode
RD is annoyed by Pinkie and tries to stay way from her until she finds out about Pinkie doing pranks
RD's brash nature is opposite of Fluttershy's shyness, in season 2 they seem like they get along well, but in Sonic Rainboom, RD only had Fluttershy come with her because she was the only one able to. She even says she wished the other could come.
AJ is a hard worker, Pinkie is a partier
Obviously they've all had their episodes where they increased their friendship with other or changed their traits up a bit, but all of that after Twilight showed up.