On Wikipedia, it talks about Nas having an era of inconsistent output. This, according to them, is right around SD-HHID. I don't really consider them a credible source of information but I have to say that to me, Nas has been all the way on point from Untitled to now. I absolutely loved LIG and I want so badly to lump it into this era of music. Another good way to divide the eras is by Lost Tape volumes. LT1 is all the way through Stillmatic. LT2 is through the Def Jam years. Of course, there are tons of unreleased songs that also fall within those ranges. With Mass Appeal though and especially while working with Hit Boi, I don't really forsee any Lost Tapes.
The "Nas picks weak beats" narrative is heavily based on Streets Discipline and Untitled. SD he released a super sparse, stripped down, anti-commercial album as an intentional statement during the height of Dips and Kanye chipmunk soul era. Like I don't need these massive, lush (and expensive) soul samples to carry me. Untitled was similar in that respect. HHID was not, but was just kind of a scattershot album.
It existed before that, because of the dusty heads mad about him not trying to recreate Illmatic. Sort of got escalated with God's Son which featured that stripped down style in places, leading to the 9th Wonder shyt. Life Is Good should've put that shyt to bed but die hard