A good alicorn OC is possible, but difficult to work with. Being able to fly and use magic is quite 'OP', but it's all in how you work with it. Look at characters like Superman, basically the most OP character ever yet written in such a way as to not be completely boring. The secret is to let your character have enough defects to allow conflict. So, sure! Make an alicorn OC! Go for it. Make her fly and use magic, shoot lazers, be a really good dancer, whatever you want. But maybe she's socially awkward. Or maybe she's full of herself because of her abilities. Get creative with it!
Here's a cool idea that definitely isn't boring. Consider the impact of an alicorn just showing up in Equestria one day. Heck, Equestrian citizens essentially equate being an alicorn with being royalty! So one just coming out of nowhere is a pretty big deal and would cause a lot of trouble. Even better, if your OC really does just want to be treated like a normal pony, having everyone reacting adversely would surely cause enough conflict to reamain interesting.
Just an idea, though. Do whatever feels right. Best of luck to all those out there who want to make a good and useable alicorn OC.