For me… standard mode (wahoo kickr bike) feels more like “real riding” but on a newly paved, perfectly flat road with a tail wind. Erg mode feels like you are grinding uphill, into the wind.
I like both… On recovery or Z2 rides Erg keeps me at the desired % without drifting too high or low. It is nice to turn off the brain and watch a show. For workouts, Erg can be really tough in those long super-threshold or VO2 reps. At least for me standard mode I can pick my gearing so I can try to keep my cadence up. 