Quick question: why Sparks/Ball Lightnings instead of Photons/RoLs? I mean, Photons and RoLs can last, while Ball Lightnings can't.
In the long run, Ball Lightnings do more damage than RoL. It takes 5 turns for 1 RoL to inflict the same amount of damage a BL can do in one turn. Generally you hold onto any extra BL that you aren't going to cremate until the last turn where it might make killing the opponent easier. It's
not required but it makes things faster over the long run.
Unupped versions of this deck I personally prefer Photons over Sparks because that damage advantage is reduced to 3 turns; which is easily doable in an unupped deck. I know some people still run Sparks to prevent them from playing a Photon and then having it get killed by Fire Bolt, Lightning, Chaos Seed, etc. but in this area it's really just a matter of preference.