Oh fuck yes! I can't believe I forgot about him! I was SO pissed what they didn't do with him and Rose. Not them together specifically, just the two characters.
But yeah, I remember being REALLY psyched about Finn, and in my head canon, the whole crux was going to be that BOTH Finn and Rey were Force sensitive, but Finn wouldn't really be aware of it at first. Which they kind of ultimately did, but not really. What I wanted to see, was for Finn to have an arc, of literally establishing connections. Since his primary character flaw was his fear, and how he was always just looking out to save himself, and then that expanded as the trilogy went on, to him caring about others, to have that expansion of his feeling of connection, be mirrored in his power of the Force. That his empathy was the key to unlocking his power. And his power, wouldn't be 1v1 martial combat (though all Force user who get a saber are at least competent), but that he would be more the Battle Meditation, make everyone around him stronger by him applying his use of the Force type of Jedi. The Jedi Consular to Rey's Jedi Guardian, if you will. And become like a central command hub for the larger war effort. Have a cool scene of him adopting a meditation position, and then show a montage of the various pilots and troops all having a similar reaction (like a glimmer in their eye, or all adopting the same facial head tilt), indicating Finn was linked in with them, boosting their performance. Couple it with more and more people developing Force abilities, perhaps with Finn acting as a catalyst to spark their latent powers. And you can still have Rey having her 1v1 with the BBEG.
But no, they decided to just reduce his plot down to constantly yelling at Rey, and simply just yelling her name. The end.