Well, like any other Evocation spell, the aforementioned bridge is purely temporary. In fact, describing it as floating rocks makes perfect sense. I don't think anyone meant it to last more than an exchange or two unless someone wishes to take the time to cook up some Thaumaturgy.
And by the way, a flaming sword absolutely makes sense as a maneuver based spell. It's basically adding a new element aspect (Red Hot Flames) to an existing object (Sword), so that as long as that Aspect remains, it can be tagged or invoked by the wielder of the sword in Weapons based melee combat.
And for something more permanent, you could indeed make a magic sword as an enchanted item that casts a maneuver based evocation on itself 1 or more times per session. Would take up an enchanted item slot like normal.
That's not what I was saying about a magic sword. I meant having a magic sword that exists solely as an aspect, not as a weapon at all. That sort of thing doesn't work well, which is why there are non-aspect things. A weak kind of bridge could potentially be modeled as an aspect, but a full, decently wide bridge would not.
Here's another way to look at it. If you have gusting winds on a scene, you can compel someone to get knocked over by them. If you have "complete, stable bridge"...there's nothing to compel there; the bridge is just a noun, a fact, a static object. (Enchanting an existing sword so it is on fire with a maneuver, could be compelled to light things on fire and the like, so that makes sense, btw). Aspects are great for a lot of things, but they aren't a great way to handle everything. A think a solid bridge that lasts for a few exchanges is not well-handled by an aspect, anymore than a solid defense is well-handled by one. Things that are more iffy and circumstantial are good for aspects.
Likewise, I'd say a net that really grapples a person is not handled well by an aspect. That's best handled as a block. A net that only gets on the guy partially and might not bother them at times is great for an aspect though. A full wall of fire that complete covers a line is not best handled by an aspect either. A wall of fire that has parts of it come in go and is a bit chaotic though, that works really well as an aspect.
Or, to put it another way, aspects are great for things that could hinder or help, but other things are better for things that always hinder or help (at least as long as they are around).