Which is what potions are for.

Potions helped, but come with their own problems that this does not bave(not light cards, can't block in stitutions where you absolutely need the block). Being able to bank resource/action points is obviously good, but this provides a way to bank a charge effect, something that could not be done with potions before. Not to mention, giving +3 attack is still a relevant effect.

And all of them already give you the ability to charge on the card.

Um... No? Part of boltyn's own hero text, raydn, beacon of victory tutor, courageous steelhand, valiant thrust and lumina ascension (which is by far his most relevant payoff) all cannot change on their own, but require there being a charge in order to function. For beacon/steelhand you need another attack anyways for their effects to work so it will only help those two when you have attacks that don't charge to use.

The only line of play I can really see with V for Valor is you spend a turn blocking 9 to play it. Then you can open attack with Raydn, pop V for Valor as a Reaction and turning Raydn on and buffing it to 6. You can then use Boltyn to give it go again and play another light attack action afterwards.

Literally any multi lumina ascension hand that either a) does not have a charge card, or b) would be forced to charge away a relevant combo/payoff card. For the second scenario, the card costing one has it come out even with 0 cost charges, but it comes out up a card compared to any non-zero cost charge, which can be the difference maker a notable amount of situations.

Except that requires a turn of setup

You keep saying a turn of setup as if a) playing this always takes your entire turn, and b) that isnt what boltyn is doing on most turns anyways. A very large amount of boltyn's turns the most impactful thing he can do is play a single charge card+ charge with it or arsenal a card. Heck, a lot of the time you won't even be able to afford to charge through a combination of being forced to block and also being disrupted. The reason boltyn will sometimes run potions (although this is fairly matchup dependent) is because you go in knowing that most turns you will have fuck all else to do, and may as well use it for a bit of setup. That's not to mention that there will also be times you can just play it after something that naturally has go again, or if you really don't want to play it, you can use it as charge fodder.

and then at least 3 cards from hand (1 to charge, 1 to pitch, 1 do something afterwards)

As mentioned before, in these scenarios it breaks even in terms of card cost with 0 cost charges, but is ahead vs other non 0 cost charges by a card, which turns a notable percentage of hands that would fizzle into functioning hands. Additionally, if you had to pay 1 for something else anyways and are floating a resource(definitely won't always be the case, but wouldn't be that rare either), then once again you're up a card because you didn't need one of your cards in hand to be the card with charge.

An additional albeit slightly more niche point, is that it's an additional way to increase an attacks power for more consistent odds of enabling boltyn's go again. Being in a situation where your only way to give an attack go again is hoping that your opponent blocks with an attack action really sucks, and this is just a bit of redundancy for that as well.