I think you're right. The reason you can see everything while in cover is the designers thought that it would be a fun mechanic. Most of the design choices tend towards realism, and this is a break from that. I really dig the cover mechanic. I dig it in Gears too, fwiw. I also enjoy the way COD4 handles cover too.
I think some R6 detractors are saying it sucks because the 3rd person cover isn't realistic, and COD4 1st person cover is. It's a flawed argument because unrealistic does not equate to sucking. In almost every other point of comparison between game design in R6 and COD, R6 is more realistic. That doesn't mean that 100 yard frag throws, long sprint time, and perks aren't awesome. They're just as "cheap" as being able to see around a wall you're hiding behind. They also make the game interesting give it depth.