Le Fanu said:
I use three!
RWS, Marseilles & Thoth.
I use four! RWS, Marseilles, Thoth, and Visconti.
No, many: RWS, Marseilles, Thoth, Visconti and many unstandardised LoS single-decks with their own systems.
It's all good. I take each deck as it comes, on its own terms.