I feed Evo canned food to one of my cats and feel it is a good food, although she doesn't seem to like the taste of it as much as other foods. It's pretty dense and gets pretty solid when refrigerated, so i find that warming it up in the microwave for a few seconds makes it a lot more appealing.
Sadie also has had weight issues and has been overweight for most of her life so far. I put her on a diet this past fall, and finally she is just about at her ideal weight. What'd I do?...cut out the dry food entirely and cut down on the amount I was feeding her. She looks great now, and I can tell she feels great because she is a lot more active and playful.
Like you said, there is no one ideal weight for cats; it depends on the individual. A cat at a healthy weight, though, should have a visible waist when viewed from the top, and when you run your fingers across his side, pressing lightly, you should be able to feel his ribs under a thin layer of fat. If you can't feel his ribs or have to press harder to do so, he's overweight.
I think you are most likely feeding too much, particularly with the dry food. 1/2 c some days seems like an awful lot. I bet if you cut that down to 1/4 c consistently you'd see him shed some of the excess weight. You're likely to get even better results if you substitute some of that dry food in favor of more wet.
If you do switch to EVO, keep in mind that EVO dry food is MUCH higher in calories than Blue, (602 kcal/cup vs 382 kcal/cup) so you will need to cut back on the amount you're feeding even more. The amount of calories in the wet food is about the same.