Strictly speaking, you are actually being overly pessimistic; a Small Laser based Blazer should just be a worse in every way other than saving 1 heat Medium Laser; 2 heat, 5 damage, Small Laser brackets, 1 ton and 1 crit (as we assume here that SLs are technically "half" a crit slot for sanity reasons), while a Medium Laser version should essentially be a Large Laser that is trading two range brackets for two less heat and three less tons (8 damage, 6 heat, 2 tons, 2 slots and 3/6/9 range)
The SL one is basically not worth using - a regular old Medium Laser is substantially superior - but the ML version definitely presents some interesting possibilities as a sort of "Inner Sphere Heavy Medium Laser" feeling weapon spread.