RE: How Good Will Steven Be?
I think the best Skyla replacement would have to be Korrina, if we're assuming the XY-on format. The only reason Steven is worse than Skyla and Korrina (in non-fighting decks) is that you waste your supporter to get another SUPPORTER. If it was just a TRAINER card, then Steven would be near perfect, snagging an energy AND a trainer card to boot! But alas, if you need to use a supporter to find a supporter you are FAR better off using N, Sycamore/Juniper, Colress, Birch's Obs, and even Shauna.
To be honest, Skyla is a tough card to replace with what we currently have in the format, but if your deck only uses Skyla for grabbing items then Korrina is the next best thing; just a shame you don't get the option to grab a stadium/supporter, only an item. But then that would make Korrina better in fighting decks than she already is!