Every engine is going to come with engine specific problems. You will also come against many general game development problems, for which the engines have come up with many different creative solutions.

I can't make it any simpler for you. You will waste a bunch of time learning stuff. The only way to avoid that is literally building your own engine that conforms to your expectations and assumptions, because noone else can do that.

There are so many invisible boring-ish problems. Ui, scaling, networking, instancing, level changing, loading screens, even scheduling etc. You need to learn to love the boring stuff, because it comes at a 10-1 ratio towards the fun-ish creative problems.

However it's best to start wasting that time today than next week.