One thing that makes me doubt it is needed is that the plug-in transformer sold by ring wires directly to the ring doorbell without a resistor. However, the resistor could be within the plug-in and we wouldn’t know.
I am aware of this solved post: https://community.ring.com/t5/Video-Doorbells/Ring-Pro-directly-to-transformer/m-p/1337
While it does state that the pro power pack should be installed, it does not state that the resistor is not needed. The reason I need confirmation that it is not needed is that other documents state that it is needed and talk about a serious fire risk if not present: https://support.ring.com/hc/en-us/articles/205180710-How-to-Connect-Your-Ring-Video-Doorbell-Directly-to-a-Low-Voltage-Transformer-Without-a-Pre-existing-Doorbell-