The only difference between bipolar 1&2 is an arbitrary definition, based on how severe the mania episodes are.

That's it. It's just a clinical definition, even within those basic categories of 1&2, there are a wide variety of symptoms and cycles.
I don't take them too seriously, the categories. I just know that other type 1 people like me, have gone to the extreme point of textbook mania..... It's pretty scary.