>>4022288T3i is definitely still a beginner camera. The i models are every bit as beginner as the non-i models, and Canon themselves classify them as beginner level. They just have a few improvements and extra features like more megapixels, tilt screen, better video, faster fps, more af points, etc.
More advanced cameras will typically have better build/construction/durability, more custom buttons, weather sealing, dual card slots, better viewfinder, and those performance gains (better af, image quality, lowlight performance, etc). Typically stuff that's more important when using the camera intensively. They may also omit a lot of the automatic functionality like scene modes, or a mode dial entirely.
In some cases, the beginner and more advanced cameras will have the same/similar image quality, but the more advanced one can do a better job of getting those shots more reliably. In other cases, there can be a big difference.
Specific to the T3i, there are a significant number of improvements and features that are common among more recent cameras. I personally wouldn't go back to DSLR's after using mirrorless, but that's not the case for everyone.
