I did check if anything contradicted the basic assumption my argument hinges on and i could not find anything, as you write the regs just mention the time set by the ECU and i couldn't find anything beyond that, additionally i did have a glance at the lap times as i don't like talking out my arse.
The article says the following:
[...] which meant he was still required to stick to the Safety Car delta time, whereas those around him weren't.
"[...] your first two laps under the safety car, you have to respect the delta time [...]" - M. Masi
No word about there being different SC delta times for the first two laps and the remaining ones, on the contrary it only says that he had to stick to
the SC delta time, whilst the others did not have to at all.
Leclerc did that lap mostly behind the SC as he caught it at the pit exit on lap 40 (was called on lap39), only half the start finish straight and Abbey were without it (look at the screencaps) - so this was effectively a lap behind the SC, not with the SC delta - you can also compare that lap time to the other laps he did behind the SC (2:47, 2:41).
I don't think there's any driver who finished a full lap with the delta times without having caught the SC yet and without doing a stop, one of those who got close to doing that is Stroll as he was the furthest car from the SC when it picked up LEC and also hadn't caught the SC train yet after pitting.
His outlap was a 2:03 (lap41) incl. the stop (~30s total) - which puts it perfectly at 30% or even below from a baseline of 95s accounting for going slower in the pits but then not being bound by the delta for a short bit between the pit lane ending and the SC line.
Various other drivers did times around 2:03 in that period on laps 40 and 41 - so regardless of whether the 2 lap limit is still a thing (i admit that i did not even know it existed) they were doing lap times which were roughly equal to VSC times, as you point out it's supposedly 30%-40% which was probably something that was estimated based on previous races (not an official number).
So yea ... i still believe there is no difference between the VSC and SC delta but i would be very happy to concede i'm wrong should anything clearly show that it is not the case.