> One caveat is that GenCast tested itself against an older version of ENS, which now operates at a higher resolution. The peer-reviewed research compares GenCast predictions to ENS forecasts for 2019, seeing how close each model got to real-world conditions that year.

And GenCast was tested against and older model which performs worse.

> The ENS system has improved significantly since 2019, according to ECMWF machine learning coordinator Matt Chantry. That makes it difficult to say how well GenCast might perform against ENS today.

And the testing makes it "difficult to say." The obvious conclusion is "run a new set of tests" but they'd rather pay of the verge to publish half truths instead.