Hey all on my game I am stuck at 69/70 achievements with I Don't Need Your Fancy Toys (defeat all bosses with only the crossbuster) remaining. My understanding was that I would have gotten this achievement while going for the "Purist" achievement. However this final achievement won't pop for me, and instead says I have defeated 5/6 of the bosses.

Any help/info with finishing up the I Don't Need Your Fancy Toys would be greatly appreciated. Thank you