There is not a single tread in this forum that doesn't turn into comparing riders to Sastre or Evans.
I can't speak for others but for me it's not about them per se (or any other former Tour winner), but about the Tour itself. And the fact it has an overbearing importance on the calendar & how riders who've won it are considered better whilst who haven't are viewed as lesser. I say this considering what it really is in physical terms: neither particularly harder nor easier than the other GT's on the modern world tour season except perhaps in terms of pressure dripping down from the sponsors & DS, because in terms of the power on the pedals to win it... it's no different (& sometimes it's even easier than its Spanish & Italian GT siblings).
For example Evans was a really tenacious "tough b*stard", i.e. that's how I remember him. But I didn't suddenly think he was a great because he won the Tour de France in 2011. It was great for him obviously, but as a cyclist he didn't go from so-so to wow at the age of 34. Just as I'll remember Roglic as a spectacular climber/puncheur with an awesome TT & one of the best mentalities I've ever seen (all sports included).
A Tour win would be amazing (especially for him), but in isolation it wouldn't change the bigger picture for me. And just to bring this back to this current season, after the Tour I had one concern only: his health (I didn't want another Pinot). But once he showed he had the legs again, all was good.
I mean he could have lost the Vuelta at any point (echelon, fall, whatever), but as long as he was performing as the Primoz Roglic we all know (win or lose), my view wouldn't change.