(Only just finished AOL myself, so I guess I'm a newbie? I wanted to read it earlier but apparently Christmas = slow shipping.)
Those are just their discrepancies as allomantic functions though, aren't they? And creating mistborn wasn't even the main function of lerasium burning, but just the side-effect, was it not? Quick skim of the Coppermind I just made suggests making an existing Mistborn burn it would do something completely different. It's basically the condensed metal form of Preservation-essence anyway, like the Well's liquid stuff and the Mists being more or less a gaseous variety, if I recall correctly. Both submerging yourself in the liquid pool at the Well as well as burning large quantities of (obviously less dense) mist managed to make Vin ascend, so maybe swallowing enough lerasium and flaring it would also cause ascension after a while? Before that occured the Mist did nothing beyond fueling all of Vin's powers at once, so perhaps that's also what lerasium's main function is? Unles for some bizarre reason a change in physical state would make it do something drastically different even though allomancy functions off of atomic structure before anything else.
It would make a bit of sense too, to be honest. Atium is essentially the all-purpose hemalurgic spike material on the flip-side of things, and the Mist made for all-purpose allomantic fuel in that one scene. Allomantic atium, on the other hand, is far from as impressive as lerasium, but in the end you are really using the "wrong" power source to fuel the system that Preservation created. And in true Ruin fashion, since Allomantic atium only shows the future up to a couple of seconds, it serves no practical purpose beyond reacting to an immediate threat i.e. combat and by extension killing people. While lerasium (and I guess the Mist if we're staying on that line of thought) in combat actually doesn't do anything remotely spectacular in the least that you can't do with anything else. Perhaps lerasium used as a spike would also have powerful but (relative to hAtium) rather "meh" and Preservation-y effects. We . . . don't know what a spike like that would do yet do we?
Speaking of, sticking to the line of thought of Mist and lerasium being a similar material like they are to the Well-fluid both god metals when used in their own shards' metallic art actually don't do anything that the normal 16 metals can't, but serve as stronger alternatives to all of them at once (queue Vin's "mist"push tearing off TLR's atium minds and flinging them out the window when steelpushes won't actually have any kind of effect whatsoever). I think they honestly mirror each other rather consistently.
Now I really wonder after all of that what lerasiumminds would store.