Compensators vs. Brass Backstraps

Adding weight and adding a compensator are very different things -- they both help with recoil control, but they do so in very different ways.
Adding weight to the frame makes the gun recoil SLOWER, which feels less sharp and is generally more manageable. It also lowers the center of gravity so the gun is much less topheavy. Personally, I really notice top-heaviness when I'm doing speed reloads. Polymer-frame guns feel "twitchy" and unbalanced in my hand. I have to actively control the angle of the gun during a reload, whereas a weighted gun moves smoothly and stays where I put it with minimal effort. 
In recoil, a weighted polymer-frame gun feels less "flippy" than a stock gun because to rotate, the recoil forces have to rotate the heavier frame. It's still rotating, just slower.
Good comps divert gas to reduce the amount of gross recoil. However, Caniks are recoil-operated. If you reduce recoil by very much, the gun stops working. As a result, most popular-market comps (speaking about all guns, not just Caniks) are grossly IN-efficient. If they actually worked, you'd need to change the springs -- and the average consumer doesn't want to do that.
Competition-oriented comps are all barrel-mounted, and they reduce recoil by such a degree that the pistol has to be re-sprung to match the specific load you intend to use in it. 
That doesn't mean inefficient comps don't make the gun feel a little softer-shooting, they do. They redirect SOME gas, but they also act like a barrel weight. That's especially true of comps that bolt to the dust cover.  The cost is the gun gets MORE top- and front-heavy -- which I don't particularly like.