I don't even think Russell's line was overly aggressive, there's enough in the video footage to suggest that - without Sainz' presence - he would have made the corner just fine, even capable of leaving space for his team mate.
This is just before contact, he is near parallel to Lewis, both of their positioning isn't far off that of Norris and the Aston, those two also being near parallel through there.
Norris managed to slow down to avoid running into the back of Russell, so it would be interesting to see the difference in speed at the point where Russell collected Sainz, or even a bit earlier.
Russell didn't just clip Sainz, it was almost a t-bone, but not because Russell came in insanely hot, straightlining the corner or anything, Sainz was the only car which was far out of the expected position, i'm sure he'll look back at this and realize he should have just taken the wide line.
Either way, realistically Russell had little chance to avoid that contact, probably even with Norris' entry/apex speed and positioning, maybe only by going in slow, potentially slower than you'd normally do in anticipation of the cars ahead not being where he expected them to be - it's still on him but he didn't do anything
really stupid or wild, it was just unfortunate.
I guess with a bit more data available the stewards came to the conclusion that he was wholly to blame but the circumstances might have played a role in the lenient penalty.