"where is the difference between DSP and CPU limitation?"
mainly the price,
but also CPU evolve way faster than DSP,
so it's about price and power, DSP system are underpowered and overpriced the day a company released it,
and that will force DSP plugins companies to make more and more compromises when native plugins dev just will take the advantage of fast native CPU evolution (with no extra cost due to an esoteric DSP management that also often force you to buy another computer).
DSP system is just an anti piracy system, since PH use one that work for 30 usd I don't see any interest in a 1500 usd dongle
just buy a 1500 usd modern computer instead