The level at the Vuelta was in fact not low. I thought it was, I will admit, and that few 'came to race' so to speak, but looking at the Angliru times, actually the riders like Landa, Ayuso, Almeida, Mas, Uijtdebroecks, Vlasov and latterly Poels were climbing at elite levels, they were just blown away by the dominant Jumbo trio.
I also think that it being Kuss' third GT in a row meant at least the opposition, if not his own team, expected him to tire at some point so took the threat of him in that group a bit too lightly, hence not contributing to the chase and allowing the advantage to become too significant. And while he did undoubtedly tire a little later in the race, it was clearly not by as much as had been anticipated by others and he was still stronger than any non-Jumbo rider such that if they'd chosen to ride for him throughout he would still have comfortably done 'a Giovannetti'. The danger was it becoming 'a Nozal' at the hands of his teammates, as it was made clear at the start of week 3 that he was a sitting duck for Vingegaard with such a minimal time gap until the online backlash forced the team to lay down the law - but due to the buffer they'd built up over other teams with their dominance, that was something that they were able to do, whereas had any opposition rider been strong enough to be a viable threat, the team would likely not have taken such a decision because they'd want to safeguard the victory, and in that circumstance Jonas and Primož are both proven commodities who have shown to be stronger on the road, whereas Sepp is unproven as a leader and his lead was so tenuous after Angliru that he may have been forced back into his usual role in the circumstances.
Chris Horner has seen plenty but you do have to filter his opinions on events like this through the reputation he has as a massive American homer, with people in the péloton attesting back during his active career that his attitudes to riders from the US and to riders from elsewhere differ significantly. Hell, he even towed Tejay van Garderen up Alpe d'Huez in 2010 in pursuit of his own teammate who was leading the race, in order to get an American on the podium. He's also made a lot of his reputation as an online commenter on the sport through controversies, such as how he came to the attention of many outside North America as a commenter for his repeated 'knucklehead' rants at País Vasco (I don't know if his channel was already popular in the US before this, but for many outside, this was the first time it really became known and talked about). So his opinion on this situation has to be viewed through that lens; he's an ex-pro with a wealth of experience, but also somebody who has always had a known US bias, and who gets more clicks when controversy is generated.
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