lol No. As Tomo mentioned, there's a difference between training and actually playing matches, U21 or not.
Games are still games and they can be used to maintain the momentum and heck, given who we have played recently, they might as well be U21 matches of sorts.
Don't think the comparison is quite on the mark. The Alonso-Chilwell was in pre-season, where the former returned early, trained and able to play matches as well to get going while the latter returned later due to the Euros and was supposedly not in the best frame of mind because of what happened at the tournament. It wasn't all just training.
Both Alonso and Chilwell didn't get called up for the September international break but Alonso continued playing because he was still in decent form then. But that went out of the window after the Juventus game and Chilwell came back straight in. He got into form, then played matches (he even scored) with England in October - Alonso also played matches with Spain - and was able to continue his momentum with us after returning.