Not really. I mean it does give you another Stardust Dragon and 2 extra junk tuners. It's good if you want the tuners and Stardust, but don't want to have them directly in the deck build
^Wrong. There is no reason to play a 22 card deck over a 20 card, the smaller deck will always be more consistent. The only exceptions are grass/mill decks. The OP is right, the skill is useless to everyone except f2ps.
Only if they decided to releases more Junk support. Junk works really fast, 22 cards or more wouldn't be a problem and Mark of the Dragon will give +1 extra deck slot.