There are currently two lv piston recipes. One added by craftweaker that takes wrought iron, in line with the other lv items, and one that takes steel from the original gtce recipes. I believe that the original was was something that was going to be removed, but was missed for this item, and that the wrought iron recipe added by craftweaker should be the only possible recipe.

I don't mind the original recipe. Small gears take less time to make, whether you hammer plates manually or use extruders/solidifiers

I have noticed this but didn't think much of it because it's essentially the same recipe, just one is Wrought Iron and the other uses Steel.

As you say, the steel version should probably be removed for consistency.

I would personally argue in favour of this remaining, as it acts as an encouragement to set up steel production due to the iron saving you can get from using a small gear (1 iron) vs a large gear (4 iron) at the cost of some coal/carbon.

Those are good points and I agree. I think the alternate recipe can stay.