Yes, I agree with your intuitions. However, we used the datasets from the official BigQuery tutorial (https://cloud.google.com/bigquery-ml/docs/arima-speed-up-tutorial). In particular, it isn't easy to generalize in time series forecasting due to the diversity of the datasets of the field. The central intuition of the experiment is that running less sophisticated methods and pipelines could be a better practice before using AutoML as is.