Of course it's not optimal, it was simply a pragmatic trade-off. This wasn't the only case with lots of paths, and the divide-and-conquer approach improved the runtime performance substantially on all of them.

What you are proposing is valid, however the “checking each intersection” part is far from a simple one. It's difficult enough with polygons only, but the input can have Bézier curves too. I highly doubt everything would amount to Log(n) - after all Skia already does something similar to what you're saying, unless I'm misunderstanding.