Welcome to Android Central! All of Verizon's phones are essentially unlocked, so you should be able to bring it to another carrier and pop in their SIM card, assuming the phone supports the other carrier's network bands.
The main reasons I can think of why people might feel ripped off about Moto's Z line are (1) no real development of Moto Mods, which was one of the big selling points, and (2) Moto's general disregard for timely software updates. By the time the Z3 was released, these two issues were well known, and you could have read up on them if you had done basic research on the phone prior to buying it.