The problem with one shot one kill is that it makes building larger ships foolhardy, and it messes up the balance between offense and defense.
I did have one idea, though it may be a bit late; make shields into deflection shields (IE, divert kinetic projectiles). This would mean that armor would be useful against lasers, and shields against kinetics.
The basic idea in my mind for deflection shields is they effectively reduce your target cross section while active, by diverting projectiles around the ship. Since shield strength scales by volume but target cross section just by area, this would have the interesting effect of giving a battleship a smaller TCS than a fighter. A hit would still be a kill, but would be even less likely on large ships.
Alternately, if people prefer shields that can be beaten down over just a reduced chance of catastrophic damage, the shield could drain energy to deflect each projectile until it ran out, then the ship dies. One is reduced chance of death and the other is x hits to kill, in the long run it works out to mostly the same results.
Before anyone claims this would make big ships too powerful, consider that the battleship would still be vulnerable if hit, and you could afford a lot of fighters for one battleship (and fighters would probably still be faster, making them hard to hit as well). I just think a game where smaller = always better would be pretty boring.