Maining Champions (help me find LoL fun again)

After 5 years of League, I feel like I'm losing the motivation to main someone. For the longest time now my mains had been Shen (before his rework), Thresh, Kassadin and since the beginning of time, Lee Sin. Nowadays I still play Lee Sin, but I'm really losing the 'fun' factor and I'm starting to get bored of Lee. Not sure whether this is related but with the boredom comes my lack of motivation to play at my best. Back in the day I used to be able to pull off really slick plays (relative to my elo at least) but now I find myself not just making sloppy mistakes and not able ti give effort, but numbing to the 'self-disappointment' you feel when you screw up as your main.

Now this rings true with just about all the champions I've listed (and then some more). As a result I'm actually stuck between not wanting to play my mains due to lack of interest in them and not wanting to play non-mains since I technically have much higher possibility of not playing them to their full relative potential. Thus I end up not really enjoying League as much.

What should I do? I really want to enjoy League as much as I did in the past couple of years but now I can't find a way to properly enjoy it anymore. Especially with so many people maining 'OP' champions it seems that I can no longer compete even in normals using champions for fun rather than champions for wins.