I don’t think that the authors of openHABian should change these statements. They are true for (small and mid-sized HA systems).
Our suggestions and recommendations are influenced by our personal experiences.
For example, I have so much stuff (addons, rules, transformations, etc, etc) running on my OH2 and I use 2 RAM “hungry” persistence services with extra bells & whistles that I can’t ever imagine running my setup on a rPi0W.
If you are planning to have only MQTTv1 and some basic addons enabled: then rPi0W will do fine.
On the other hand… If you want to enable advanced stuff (for example: Homekit/Google Home/Alexa on top of Hue and KNX), I would recommend something as powerful as the rPi2/3.
If you want to enable even more stuff (e.g. InfluxDB with Grafana) I would consider a NUC (to avoid SD card I/O).
It all depends how many subsystems you will enable in your HA system powered by openHAB2.