Notes:

I tried to find people discussing about the difficulty of the bosses on X Dive, but I found no one, so I built my own tier list of difficulty.

You can change almost anyone of their places, but I will defend the fact that Shurikein is superior threat.

BTW you should check out Mega Man X Dive, they are making cool art of older bosses and characters.
It clearly is a Gacha game though.