I just tested both my iPhone and iPad via both airplay with an older AppleTV and with the dongle (new version). With the iPhone (7 plus) to the AppleTV I found was having issues with bluetooth dropout (in this case both Wahoo HRM and cadence). Also you lose the sound when going via Airplay.
Here in the US I found that Walmart has the new model Lightning to HDMI dongle for $39 US so I picked one up yesterday. Brief tests with both iPhone and iPad worked very well (but they were brief).
Today I rode the flat Watopia loop as an iPad test. The iPad was connected to the TV via the dongle. It worked very well! No bluetooth dropouts. I did find that the iPad did not charge (not sure why…still need to research that). You do get sound with the dongle. Refresh rates are not what I get with the Macbook Pro but they are very good. Since Zwift is using screen mirroring the 4:3 aspect ratio of the iPad does not fit a typical widescreen TV … you get black bars on both sides. All in all, this was overall a very acceptable solution.
Later today I’ll test the iPhone 7 plus on a ride with the dongle.
I think the MacBook would be the preferred solution for long rides.
Also, I’ve not tested anything like Discord running as a background task under IOS to see how audio works.