Yes, I did adjusted the shutter speed, and I still get some blurred shots or less color or light in shots.
That's exactly what happens. A lower shutter speed will allow more light to touch the sensor but the image will be more prone to blurring. Conversely, a higher shutter speed will reduce/eliminate blurring but as less light can hit the sensor, the image will be much darker.
There are two practical solutions that can resolve the issues of using a high shutter speed without changing the body:
- Use of a flash at higher shutter speeds (or throw more light at the subject)
- Use of a faster lens i.e. one with a larger aperture or lower f/stop number
The EOS 600D is perfectly competent at landscape photography and it allows you to adjust the colour balance.
You shouldn't always rely on numbers as an indication of how good the AF (or any feature for that matter) is. 11 vs 9 doesn't have to equate to better. In the real world, the extra AF points available on the D5100 may not necessarily give it at an advantage over the 600D.
A lot of the time with DSLR photography, very little of "how good" the picture turns out is determined by the body but rather the lens being used and the person taking the photos.
Whether you should stick with Canon or not is a hugely personal decision and I don't feel anybody here is qualified to give you a conclusive or definitive argument to stay or switch. Things from the way the camera feels to navigating the camera's menu are things only you can decide on.