TImage is not optimized for game programming, it is slow.
I couldn't agree more even if I wanted to.
imho there is only one small caveat: you do not know how slow unless experienced that yourself.
In my opinion using images (TImage) for grasping some of the concepts that are used for/by games are more beneficial. The things you learn from that (positioning (all axis), collision detection etc) can be used later on when switching to direct canvas/bitmap drawing or even when using a dedicated graphical engine.
I do not know anything about what TS is working on but as long as it does not require much speed then it also does not matter much (e.g. there is no need for speed for a game of chess/checkers).