Removing attack rolls from attacks

I guess this serves as my introduction post. I've been playing tabletop games since D&D 4th ed came out and have really stuck within the D&D genre of RPGs until recently.

I'm currently working on a superhero RPG and I'd like some thoughts. It started out as a revision of D&D 4th ed but has evolved very significantly since then with very few vestiges of 4th ed left. In my latest iteration I'm looking at removing attack rolls and on,y rolling damage rolls.

I love Wild Talents' One Roll Engine but find it a bit complex for what I'm aiming for. I'm looking for a game that is about as simple as 13th Age or D&D 4e. I also want to retain hit points as I feel hit points as an encounter resource match the comicbooks quite well.

I'm using combat related ability scores (called primary scores) that range from 0 to 5. The ability scores are currently:
Initiative: Helps determine who goes first.
Resolve: Determines HP which include both mental resolve and physical stamina.
Physical Resistance: All physical attacks go against this resistance.
Mental Resistance: All mental attacks go against this resistance.

The way the defences work is as DR. So any damage rolls made against them are reduced by that value (minimum 0). So if we had a physical resistance of 3 then you would need a roll of 4 or higher on the dice to deal damage (a roll of 4 would deal 1 point. A roll of 5 would deal 2 points, etc).

I'm proposing that rather than remove the attack roll, we remove the damage roll. Multiple attacks would be represented by multiple dice. Here are some attack options and the damage they use. Each attack is a standard action:
Grenade: 1d4+1
Gun: 4d4
Bow: 1d8
Flamethrower: 1d6+1
Flurry of Blows: 3d6
Sword: 1d12

On a max roll you score a critical hit which let's you add +1 damage which at this scale should be significant.

So in this system when you use a standard action to attack with a gun you get to fire 4 times in the time that a bowman fires once. This has the benefit that physical resistance 5 makes you bulletproof.

Here's the DPR when attacking against physical resistance 3 with 12 HP

Grenade DPR: 1
Gun DPR: 2
Bow DPR: 2
Flurry of Blows DPR: 3.5
Flamethrower DPR: 1.29
Sword DPR: 3.83

In this you need at least two rounds to take down the enemy with 12 HP, even if the swordsman rolls max damage. Melee should deal the most damage as they're at the most risk while area attacks should deal a third of their respective type (whether Melee area or ranged area). The names of the attacks would be abstracted in the actual rules. This is just examples (e.g. Gun would become Rapid Fire).

What do people think of it? I'm worried at higher levels about rolling a fistful of attack dice and a fistful of damage dice. This reduces it to just a fistful of damage dice (although under this system I'm not convinced HP would scale with level. I need to investigate that). It also gets around the issue of rolling a critical hit, but then rolling poor damage.

I'm interested in hearing people's thoughts on the proposal.

Removing attack rolls from attacks