In looking at the photo of the brace (no shoe) it looks like there is a pivot point with a bolt right on the ankle bone. If you want t know if your brace is good enough, (and I am really not trying to sound sarcastic) have someone lay your 400#+ motorcycle on your ankle and see if you have a hot spot on the ankle bone. That's the thing about the ankle support and protection of motorcycle boots - they are meant to spread the impact and abrasion out, and not have a focal point. Looking at that, I would almost put money on the brace doing more damage if the bike were to land on it, just because you have all that force focused on a tiny area
Get a good pair of ADV or off-road boots - there is a LOT of support in them. And as you said, there are plenty of posts going over boot choices.