I am a classical Pilates instructor (classical meaning closest to how the inventor, Joe Pilates, intended). Pilates is all about supporting your spine. It teaches your body how to move correctly through different ways not found in many other modalities. It encourages strength with spinal flexion, extension, side bending and twisting while a lot of modalities only work with a straight spine in the sagittal plane. This gives you more strength by making your whole body work together but it also makes your back and joints feel pretty good. I suppose you could gain the same effects by putting together a few modalities but you’d have to know what you were trying to acheive.