I don't own a large heavy skillet - the one I do own is small and can't hold much. Is using my Dutch Oven on the stove a reasonable replacement, if I leave the lid off?
It depends on what you're doing with it, but for the most part, yes. Things like giving it a shake/toss to move things around will be more difficult, unless it's one with a long handle on one side, but you can just stir instead. Also, lifting to pour stuff out of it will be more difficult.