Guys, I have this.
Anyway, let me assume that you have Blazekin, because that 7th gym is easy for people wih Sceptile and Swampert, due to most of their Pokemon being ground or rock types.
Correct me if I'm wrong, but I do not believe you have to beat the 7th gym for team magma to appear at the rocket station, so if I'm right, do that to continue the sotryline and level up your pokes.
One last thing I suggest is to go around the sea challenging trainers. Most will have water Pokemon (It'll be a challenge if you do have that Blazekin) so if Im right, that will help Exp wise.
Btw after you beat Magma, Aqua will take the sub and when you defeat the gym, you can go underwater to Kyogre's cavern, and that will trigger kyogre & groudon battling.