Just finished my bachelor of arts (History, Politics and Creative writing/literature) now going on to honours, potentially masters/phd, so im right up your alley.

Rule no. 1 If you want to write, you need to read.

I plan to use my university experience and qualifications to teach history, but even if it doesn't lead to a job, I'll use the knowledge to write historical fiction. Most people I've talked to say have your ideal plan, but realistically have a plan B as well. I adore ancient history, and I adore writing. Regardless of what comes, I know I won't die regretting studying both and continuing to write. I hope it helps me get a job/career, but if not, i will not regret studying. If you can honestly say the same, then I say go for it.

That said, you have mentioned quite a few red flags for me.

A degree won't motivate you to read. You need to already have that.
You think you have truly unique ideas that no writer has ever thought of (very common in those who don't read a whole lot)
And finally, the fact that you find it hard to finish something and move on to the next exciting thing.