KG was never the offensive player that Cousins is.
I'm looking at the numbers and I am just not seeing any evidence of this.
I'm not sure why you are struggling so much.
In KG's entire career he has averaged 21+ Points Per 36 only twice - in 04/05 and in 05/06. Cousins has already managed that in four out of six seasons.
KG's career high was 22 Points Per 36 - Cousins has just put together three straight seasons of 25, 25 and 28 points Per 36.
As far as offensive efficiency, KG has a career average of 1.23 Points Per FGA. Cousins has a career average of 1.26 points Per FGA and hasn't even reached his prime yet.
That number is only going to go up since he added a three point shot, as evidenced by his 1.32 Points Per FGA this year.
Cousins' career Free Throw Rate of 45.2% is in an entire other realm compared to KG's of 29.3%.
In fact Cousins' lowest ever FTR was an outstanding 37.3%, and KG has matched that only 3 times in his entire career.
Cousins has now added the talent of being a legit three point thread, which makes him quite possible THE most deadly inside-outside threat in the NBA. KG has three point range, but he was never a real threat from there to the point where defenders really had truly respect it, or coaches had to truly gameplan against it.
KG is probably one of the greatest midrange shooting bigs ever to play the game, one of the best passing bigs ever to play the game, and he was also an excellent finisher around the basket. However his game as also very strongly focussed on finesse and athleticism, and as his physical abilities faded, so to did his ability to consistently carry an offense. In his later years in Boston he rarely played in the post, instead tending to settle for long midrange jumpers - which he did hit at a nice rate, so that allowed him to remain effective (if not dominant) offensively.
Cousins doesn't rely on quickness and athleticism - he's all about size, power, skill and brute strength. That stuff sticks with you as you get older, so I feel he will probably age better than KG if he learns how to control his emotions. The ability to overpower guys in the paint combined with his ability pass and step out to the three point line is an impressive combination - it should allow his game to age very gracefully.
When looking at KG's stats you need to be very careful not to be caught up in raw numbers. KG played in an era where teams were not stacked like they are now, and so start players tended to play massive minutes. Like many guys at the time (Vince Carter, Tracy McGrady, Kobe Bryant, etc) KG was playing up around 40 minutes a night during his prime years, and that elevates his production.
Now days barely anybody plays those kinds of minutes, and Cousins tends to be only around the 32-34 MPG level. Once you adjust for minutes played, KG's scoring numbers are not even close to DMC's. You're talking about a guy who peaked at 22 Points Per 36 versus a guy who is currently average 28 Points Per 36 - that's offensive production on a whole other level.