We haven't even been able to come to a solid conclusion in the equestrian world yet as to whether SMB's and/or polo wraps even offer real support and so it's impossible to conclude if they would weaken the legs at all.
I'm inclined to believe that the protection a good all around boot like an SMB offers is going to outweigh any potential negatives. They may or may not offer support, but they obvious offer good protection from general outside leg injury and help keep the lower legs warm and circulating.
However, I even find the ankle brace analogy a little silly. How do we know this? Have we done a study where a perfectly healthy human wore a leg brace for a year and proved weaker then someone who didn't? Typically people wearing these types of devices are those with already established problems.
And on that note, it's the reason why Zierra wears them and Jynx doesn't. They help with Zierra's leg swelling, whereas I see no reason for Jynx to wear them - she just wears bell boots for clipping.