Absolutely none of this would be contended if they just did that.

This view conflicts with fairly broad reporting of precedent around similar situations that were recently ruled to be allowed:

From The Race:

After Norris was involved in a similar incident in 2020 at the Italian Grand Prix... he was cleared of any wrongdoing...

But it [creating a gap under safety car for a double-stack] has continued to be a known practice in F1. A recent example was this year’s Azerbaijan Grand Prix, where Lance Stroll backed off behind Aston Martin team-mate Fernando Alonso so much that George Russell attempted to overtake him in the pitlane entry.

Norris’s penalty hints at there finally being an explicit change in how this action will now be viewed and dealt with, or that there was something specific about this incident that made it unsporting when other cases are not.

The stewards’ verdict does not explain this. The FIA has been approached for comment.

From Brundle's weekend debrief:

Even rival team managers were telling me post-race that it's been normal and accepted behaviour to build a small gap behind the Safety Car before a double team pit stop for a few years now, which indeed was Lando's firm view.

My read on this is that both the justification and also the decision itself were irregular. While it's perfectly reasonable to tighten up enforcement around creating gaps, I'd say the change should be announced in the race-director's notes prior to a change in interpretation being enforced.