100% agree and while I don't think I could come up with any better examples, even the ones you are making really didn't have that similar of a level over 3 years.
Contador was way better than Schleck in 2009, they were almost equal in 2010 and while Schleck might have only been better in the 2011 Tour because Contador had the Giro in his legs, he wasn't even able to beat Cadel Evans that year.
Froome meanwhile was clearly superior in 2013, we didn't really have a comparison in 2014 and then they were pretty equal in 2015. I'd honestly take 2016 into consideration too although Quintana was nowhere near Froome in that Tour, just because he beat him a month later at the Vuelta.
But the key takeaway is, even in those rivalries there was at best one year where they were equally matched. I mean if you consider something like 2009 and 2013 you would have to consider 2021 as a level of similar performance for Pog-Vingo as well. And to be honest in 2010 and 2015 I was absolutely convinced the respective rivalries would go on for some time when in fact their peak had just passed.
You know, people on this forum have often (and rightfully) joked about a post I made before the 2020 Tour where I announced that Pogacar was overrated and in fact not the next big thing. My main point at the time was that people were calling young gc contenders the next Indurain/Armstrong/Froome way too fast and that the guys who actually go on to dominate are never the hyped up youngsters but some guy who comes out of nowhere. My examples for two such riders were Bernal (who at the time was even higher rated than Pog) and Pogacar and while I was spot on about former, I wasn't about the latter. That being said, the reality is, the jury for just how wrong I was about Pogacar is honestly still out, and Vingegaard might be the guy coming out of nowhere I was thinking about. I certainly did underestimate Pogacar but my prediction that he won't be the next gt dominator could still become true because, as you said, in cycling one only ever knows who dominates after he has dominated and never before.