I'm a Fed fan but I think Djokovic is underrated. Everyone, even those who don't follow Tennis, know who Federer and Nadal are. Djokovic, on the other hand, isn't as popular or celebrated for some reason. I usually cheer on Djokovic as long as it isn't against Fed. He deserves to be appreciated IMO.
I also think we, as tennis fans, are lucky to live in an era where the three greatest players of all time play in the same period. This is the big reason while I hate the term "Big 4", it somewhat undermines their legacy to group them with a dude who isn't a GOAT-candidate.
Also, I think Thiem is a greater threat to Federer and Djokovic than Nadal is on hard court. Nadal hadn't beat the other 2 off-clay since forever. Thiem actually has a winning record against both of them these last 2 years, IIRC.