The H2S and H2D share the same fundamental hardware: same chamber heating, same max nozzle temp, same speed, same AMS. The H2D adds a dual-nozzle switching toolhead for two-material printing (not just multi-color via AMS) and support for the higher-power 40W laser. Both machines accept Bambu's optional 10W laser and cutting module, so basic engraving and cutting is not exclusive to the H2D.
If you need soluble supports for PA-CF parts with complex internal geometries, the dual nozzle is genuinely useful. If you want laser engraving or light cutting, both models take the module; the higher-power 40W upgrade runs on the H2D (and the H2C), not on the H2S. If you need neither the dual nozzle nor the 40W laser, you're paying $350 (street) for capability you'll never use.