After Djokovic dominated Rafa in 2011-early 2012, Nadal went 6-1 vs Djokovic during MC12-USO13, then Djokovic started dominating him again till 2017 and now both of them dominate each other on their best surfaces.
Just like after Nadal dominated Federer in the first half of 2006, Roger went 5-2 vs him in the second half of 2006 - 2007 before getting dominated again in 2008 - early 2009. So there indeed have been swifts in Big 3 rivalries, I don't know why you deny that ? Dunno what school you're talking about, but if it taught you Fedr was better than Rafa in 2018-20 based on an inexistent HC H2H between them in this period, then it's probably not a good one.