While Forza and GTS simulate different things, they're both mid level Sims with a good ease-of-access physics system that resembles real-life, but can be very forgiving too. They've always been aimed like that and have always sat at mid level. Not as demanding or simulating as much as Pcars or Assetto while still mimicking reality enough, but also not being so forgiving that it can be considered in the same spectrum as arcade games like NFS and Horizon.
They sit in the middle, having a nice balance in my opinion. Hence the term sim-cade - not to be confused for an insult. They're built to be accessible but with a good grounding in reality.