Edit 1: Fixed some numbers because of cards pointed out by commenters where timing doesn't work
Edit 2: This review is now somewhat obsolete as we've had an infusion of Superpower-traited aspect and basic cards in the most recent hero pack release. There are too many details to get into here so another review might come along one day to reflect on this change. I will keep this updated with the hero-card counts though.
Edit 3: With so many heroes now, I split it into 3 tiers. Tiers 1 and 2 previously were combined as Tier 1.
Latest heroes: X-23 and Deadpool
Deft Focus is the strongest, though most restrictive, non-hero resource generator we've seen yet due to is low cost of only 1 resource. All current Superpower cards are hero cards (except Invulnerability, which is horrible), so you can't actually build a deck around Deft Focus, but some heroes will benefit from it more than others. (See Edit 2)
Here is a list of heroes ranked by how many of their cards can take advantage of Deft Focus. Obviously, this excludes cards like Fruition or Speed of Light that are Superpowers but zero cost. Some superpowers that are interrupts during the villain phase are also not counted since Deft Focus is used as an action, not a resource.
Tier 1: Auto-include
Quicksilver (13), Groot (12), Vision (10), Spider-Woman (9), Shadowcat (9)
- These heroes' superpower cards are plentiful and strong, so you will activate it virtually every turn. Focus is one of the best cards in your deck. You can consider playing 2 copies just to make sure you see it early. Probably not 3.
Tier 2: Usually include
Spectrum (8), Rogue (8), Adam Warlock (7), Colossus (7), Storm (7), Cable (7)
- I added this tier in Edit 3 more to highlight the Tier 1 heroes rather than to downgrade these, and the top edge of the tier is certainly fuzzy. I would still play 1 copy of Deft Focus almost all the time.
Tier 3: Might consider
Hulk (6), She-Hulk (5), Wolverine (5), Gambit, (5), Thor (5), Captain Marvel (5), Ms. Marvel (5), Scarlet Witch (4), Domino (4), Spider-Man (3), Iron-Man (3)
- While these counts may be low, remember it only takes 2 uses of Deft Focus to break even. Some of the superpower cards are really powerful too, like Scarlet Witch's Hex Bolt or Iron-Man's Repulsor Blast, both of which decks will want to play many times in a game. I would think about playing either 0 or 1 copies of Deft Focus.
Special case: Nova (6)
Nova's count is high enough that I might run Deft Focus, but if you consider how Nova plays, it is not actually necessary. Pot Shot and Lightspeed Flight get paid for easily by Supernova Helmet or Connection to the Worldmind...no need for a cost reduction of 1 if the resource you are paying gets doubled automatically. I personally would not play a Focus, but you wouldn't be crazy to.
Hope you like my breakdown, and let me know if you've tried it and found success with the lower count heroes!