1. It is not redundant and it is diverse. For action, they have the three Ben 10 series, Generator Rex, Hero:108, Metajets, Totally Spies as well as The Amazing Spies, Star Wars: The Clone Wars, and they're about to have Sym-Bionic Titan, a Young Justice cartoon, and a new Thundercats series.
For comedy, they Adventure Time, Chowder, Flapjack, the Total Drama series, 6teen, Stoked, reruns of Kids Next Door ,Courage the Cowardly Dog as well as Ed Edd and Eddy and Scooby-Doo, plus the new Scooby-Doo series Mystery Inc. How is that not diverse? Plus, a number of the above have good ratings, how is it redundant?
Why does it matter so much whether the main characters of a cartoon are kids or in school? Children identify more with characters around their age. Besides, this isn't just how it is with Cartoon Network, it's the same thing with Nick and Disney currently, and has pretty much been like this for the last few decades. It may be nice to have a couple of comedy cartoons with only adults, but how far could they really get with young demographics?
2. The Secret Saturdays isn't a comedy like Spongebob or Rugrats, though. If a series does poorly, or if advertisers are not satisfied with how program is doing in the timeslot their ads are sponsoring for, than of course it's going to fizzle out on the schedule.
However, it should be noted that The Secret Saturdays isn't the only example. Aside from Spongebob, Rugrats, and possibly The Fairly Oddparents, has Nickelodeon given any cartoon a real chance? Can we say for sure that The Penguins of Madigascar and Fanboy and Chum-Chum will last longer than Danny Phantom or The Mighty B?
To get back to Cartoon Network, it should also be noted that while Chowder was canceled, it didn't phase out on the schedule like TSS, in fact Cartoon Network still aired promos for new episodes of it, and it's even been in reruns frequently as today.
3. (You didn't have a three, I'm just adding a three for convience

) If they did that have that much faith in Unnatural History, it would stay on it's original timeslot on Sunday. Putting it on Tuesday which has not even been used before isn't going to do much for it's recovery. Just because it may be a new episode against a rerun on Nick and Disney doesn't mean it won't have competition.
Besides, they took off a number of reruns for it, and haven't mentioned it in their rating reports. And if Cartoon Network is only pushing live-action, then why did the animated program announcements far outnumber the live-action ones? And why did they recently cancel all their live movie projects???