The general idea to give weapons different crit effects is nice. Though I don't like your specific examples.
In a general note. I used to consider rocket launchers to be weak and underpowered. I changed my opinion on those however. Rocket launchers have three distinct advantages over other BG weapons:
- Their shots cause knockdowns on anyone without stonewall.
- Rockets can safely be fired without hitting teammates (this is a big one).
- Rocket launchers have a large range
The above makes a rocket launcher a very powerfull support weapon. This alongside the fact that rockets deal okay damage makes them very deadly.
Deathlines, stunning and their far range allow rocket launchers to easily deal with many builds, and still retaining some use when facing full tanks due to their okay damage.
So rocket launchers really need no buff.