It is well known by most of us here that unstable weapons dont do much damage unless based on high crit chance.

A chance for a higher damage number, doesn't automatically mean DPS is also higher ...

Example

Stable weapon

1 damage, 33% crit chance for double damage.

1. 1 x2 Crit!
   
2. 1
   
3. 1
   

Max damage: 2
Average damage with 3 attacks: 4

Unstable weapon

0-2 damage, 33% crit

1. 0 x2 Crit!
   
2. 1
   
3. 2
   

Total: 3 damage

1. 0
   
2. 1 x2 Crit!
   
3. 2
   

Total: 4 damage

1. 0
   
2. 1
   
3. 2 x2 Crit!
   

Total: 5 damage

Max damage: 5
Average damage with 3 attacks: 4

Increasing crit chance doesn't change this.

With unstable weapons you sometimes 'waste' a crit on an enemy with low health though. So statistically the dps will be a tiny bit lower depending on who you fight.

Unstable is for those who like seeing big numbers.
And if you can't defeat a boss, then you might still win using unstable if you get lucky.