DarthSpectrum

I think you can beat the game with any combination of pokemon. That being said, without giving too much of content away, your team does seem ill-suited for some of the up coming battles. Consider getting a Magnetzone, Ampharos, or some other electric type pokemon. You will need one of these to fight the flying type gym leader and one of the PULSE pokemons. As well, if it is possible, breed another Ralts but evolve it into a Gardevoir instead. A powerful fairy type will help tremendously in future battles. Getting an Ice-ground type such as Mamoswine will also be useful. You will end up fighting a lot of powerful pokemon with 4x weakness to ice and 2x weakness to ground. Again, it is up to you to decide which pokemon to run in your team. However, I strongly recommend getting powerful Fairy, Ice, Steel, and Electric type pokemon to deal with some of the future battles. Don't forget to designate someone on your team to put down status effects. It is almost impossible for you to beat the most recent gym leader without employing some tactics with status effects. The gym leader has 2 pokemon with base stats around 600. None of your pokemon at that point will be able to fight toe to toe, you will have to spam revives/cotton candy as you wither it down with either status effects or with pokemon moves used under Trick Room.

Hello, Your team comp is already pretty decent. Consider getting a Magenton / Magnetzone to replace Garbador. (Shade's gym) I don't want to go into detail of further episodes, but having an electric steel type will make your life A LOT easier. Magnetzone can deal with half the PULSE and gym battles later on. I really like your Gardevoir/Meowstic. Consider teaching them trick room and light screen to deal with enemies that can out speed you. Meowstic with the prankster ability can also provide great utility to your team, but the TMs for Thunder Wave and Toxic haven't been released yet. Keeping Gardevoir on your team will be a must, unless you can get some other fairy type pokemon to deal with dragon type enemies. As well, switch Gardevoir's ability to telepathy. It will be useful in a few of the future gym battles. Donphan isn't that bad of an option. Earthquake will be tremendously helpful in two of the future gym battles. If you really DO want to replace it, consider getting a Mamoswine as a general pivot and stall. In future gym double battles, send out Magnetzone or Mamoswine with Gardevoir and spam Discharge/Earthquake. You can make short work of most enemies.