Edit: Fixed some numbers because of cards pointed out by commenters where timing doesn't quite work. Updated with new heroes up through Ironheart/Nova.
This 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. (This may be changing in the future. The recently spoiled Sp//dr has a few protection aspect cards that are superpowers)
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: close to an auto-include
Quicksilver (13), Groot (12), Vision (10), Spider-Woman (9), Spectrum (8), Adam Warlock (7)
- Deft Focus is amazing with these heroes simply due to how many Superpower cards they have. I would always play 1 and consider playing 2.
Tier 2: warrants consideration
Hulk (6), She-Hulk (5), Thor (5), Captain Marvel (5), Ms. Marvel (5), Scarlet Witch (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 (8)
Nova's count is high, but if you consider how Nova plays, Deft Focus is not actually necessary. 6 of these cards are Pot Shot and Lightspeed Flight, which get paid for 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. Also, the 8 count doesn't include Forcefield Projection, which is mostly meant to be played in the villain phase but could have some niche uses with Toe to Toe or retaliate villains. So I would understand if a Nova deck does want Deft Focus, but it is not an auto-include just because he has 8 superpowers.
Hope you like my breakdown, and let me know if you've tried it and found success with the lower count heroes...especially Nova!