I used to agree, but after I saw someone (earlier this year I believe) with an Ahrefs screenshot of a website (possibly his site, but I don't remember) with 1000s of RDs and 100% d0follow backlinks getting millions of visitors per month I kind of changed my mind a little...
Although, it's possible that - in google's typical fashion - they have rules and exceptions for everything, so it's possible that the site had been so trusted by google that they've let it get away with it.
But yeah, sometimes you can get away with 100% DF links, but you're right, it's best to have a mixed profile in general, just to be on the safe side of things. Not everyone is as lucky as that dude