I agree on the whole, except I'd say:
About 6 contentious punches were thrown in that last round, I thought 2 were legal, 1 was borderline and 3 were clearly low (1, before the big right hand up top, which started Sergei's moaning, and then 2 in the final finishing sequence).
Sergei should have thrown a few low blows back and forced a ref intervention, but like you said though, he was fading, and in my opinion, looking for a way out. Ward obliged him with a few cheap shots. It was a BS decision by Weekes not to even give him a standing 8 count. A big shame for boxing.
Before Kovalev was hit by the big right hand, he was hit with a borderline shot. He was too busy complaining about that one (and looking for a way out), when he got rocked.
Still, he was looking for a way out and Ward gave it to him with a couple of low blows. (1 borderline, 2 were clearly low).
A couple of noticeable things though. Whilst Sergei was leading on my scorecard by 2, he was visibly fading in the fight and Ward was actually starting to walk through his shots. I think he would have stopped him eventually.
Sergei was looking at the ref for help, probably feeling the tide was turning or he was running out of gas, when he really should have just thrown a couple of low blows back at Ward and forced the ref to step in.
The stoppage itself was BS. He should have got a standing 8 count, at least. It's left a cloud over the fight, and that's not good for boxing.