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What is deft focus doing here? Is it just for repulsor blast?

Yes. It's a cheap 1 cost card, that when played, basically gives you 0 cost Repulsor Blast. It's not fancy, but when you can use a Repulsor Blast for free (especially early in the game, when all the resources are important for setting up) for what's almost a granted 3 dmg (but usually more), it gives you some options. And of course, it provides Energy resource. This deck is all about giving you options, depending on the situation

Why not play something like helicarrier quincarrier or avenger's mansion which can pay for anything for only 1 more resource (or 2 but you get a draw instead of a resource)

None of those are Energy resource cards. This deck was studied with Solo in mind (I'd love to receive feedbacks on how it performs multiplayer or solo multiple hands, because I didn't have the chance to test it). If you've ever played Iron Man solo, you know that you can't waste turns or setup time. 3/4 setup cards are a no go if you want to stay in hero form. If you can play one of those cards early on, it means your missing on playing tech cards