The title says it all but I ask because while I love wukong and I understand I'm not good at the game and etc I feel like I'm holding myself back a bit by not playing someone like Gragas in this current meta. I just want some advice because my interest right now is getting good and climbing back to gold and then even up to diamond.
You have to really like that champion or it's lore. That's why i love playing sion i love slaughtering my enemies and bathing in their blood
by having fun while playing them. which is really easy because i play 
You should always learn to play multiple champions, that only makes you better. But nothing stops you from going back to your main from time to time.
play someone you like, id never play that fatty gragas bc i just don't like him, the power of your main will give you power
I don't perma main anyone. I change mains every so often.
Playing the same over and over gets boring, and also sometimes meta just makes some champs lives hell.
why would you play only one champion ? you are only playing around 0.5% of the game.
You can get to gold playing Wukong. You could also get to gold by switching to Gragas. I don't think either option is significantly easier. You should pick something you enjoy because it will probably take quite a few games to climb, especially if you want to get to diamond.
If you do decide to stick with Wukong, work on learning everything about him. Read his abilities on lolwikia. Read guides on lolking or mobafire. Watch streams of high elo players playing Wukong. Think about your build and whether there's anything you can change to make it better. Practice your first clear in custom games to make it more efficient.
Whether you keep playing Wukong or you switch, you should work on becoming a better jungler in general. Watch the minimap to see where the enemy jungler is, and try to see good opportunities for ganks or counterganks. Ping before you get to the lane so that your teammates can prepare for a gank. Pay attention to timers so that you can contest objectives and clear your buffs efficiently. Work on vision control.
If you learn your main and you learn your role, climbing will be easy even if you play a champion that is outside the meta.
