Seis is much better without Laserbank. A pure lock version is amazing. Its only bad matchup is Yveltal (Which the laser version loses to anyway). Against Metal and VirGen it is 50-50, and better if the VG doesn't run Manectric, and better v metal if they run less than two Cobalion EX. Everything else is a highly favorable matchup (Donphan, Aromatisse, Plasma, etc.). I lost in top 4 to metal with 2 cobalion because I drew bad in game 1, and I played badly game 2. I tested against a version with three cobalion and won every game (only like 2 or 3, with no dead draws or stupid hax on either side).
The only Pokemon I play are 4 seis, 2-2 Garb, and 1 Jirachi (MVP not as bad to start it as with other decks). Yveltal is a bad matchup and there's no way around that.
You don't need techs or extra poison damage if the opponent is stuck not able to do anything the whole game.
Fire attackers are unnecessary in pure lock Seis.