Right, jokes aside I should have thrown something useful here. I don't think I've ever had a team of 6 that just beat everything and anything, intense mode asks for a specific strategy from time to time. You can get a lot of help on the forums for when you get stuck too.
Fennekin alone is probably enough for the first gym with Psybeam at level 17. There's no way you should pass on Rockruff, definitely get one of those. Always thought Vivillon early game is quite useful as well (another psybeam level 17). Xatu is your guy for the second and third gym. I would use Hariyama as well, bulky and strong (not to mention it makes a mince out of Angie) I have no freakin' idea what straight out beats Narcissa, use to be Pyroar. Maybe Woobat can, you'd be suprised how useful that little fucker can be with Simple ability. Valerie I heard gets pummeled by Amoongus which can be found in the same jungle where the battle is. Maybe a Manectric can help out. Maybe you turned your Eevee into Jolteon? I don't know, smoother sailing involves Blaziken against everything (Blaziken blasted even Valerie in my case)
I mean you get the idea, there is a solution for every single gym battle prior to that battle, just gotta be creative and figure it out. Who knows, maybe Mystery Egg drops you an Axew and solves everything right then and there.