I've always felt strongly the 4th round is the cut off pretty much. You don't always expect 4th rounders to be great players but you expect something. I tend to think of the draft more as by tier than by round.
Tier 1 - top QBs... usually between 0-2 picks a year. These are guys like Manning or Luck you pretty much know will be good. These guys are in their own catagory of value.
Tier 2 - Top talents and talented QBs 2-10 picks a year. These are players that are super talented and usually very safe. Sometimes this includes non-skill players who tend to fall. Also QBs who have a very good chance to hit. Guys like Bosa - DL, Adams - S, Nelson - G, Mayfield - QB, Quinnen Williams - DL.
Tier 3 - Talented and probably safe players. 10-20 picks a year. These are guys who should be good but are outside of top 5 consideration. Sometimes they injured guys in the first catagory. TJ Hockinson - TE, Jeffrey Simmons - DL, Gronk - TE, Myles Jack - LB, Minkah Fitzpatrick - S. Guys like these can even sometimes slide outside the first, though they shouldn't IMO.
The first 3 tiers are or should pretty much always be in the first round nearly entirely. The 2nd tier usually (not always but 95% of the time) starts at the end of the first and goes well into the 2nd or even 3rd.
Tier 4 - Very good player... but. These are players with a 'but' at the end. Maybe they didn't play long enough? Maybe they played bad competition. Maybe they had a few bad games. Maybe they are believed to be missing one aspect of their game. Maybe they just weren't dominate enough or have perceived upside or elite physical traits. Ect. Those things aren't always true, but many teams and scouts claim them to be there. These are guys like. Sony Michel, N'Keal Harry, Joejuan Williams, Chase Winovich, DK Metcalf, Deebo Samuel. This year there were a lot of these kinds of players.
Tier 5 - Good players... but. These are basically just like the other group of guys but seen a bit lower. This group goes between some part of the 3rd and 4th round. Sometimes all the way through and into the 5th. Sometimes ending at the end of the 4th. These players are often seen as role or specialty players. Limited starters or have big red flags. Damien Harris, Hakeem Butler - WR are some examples.
That's how i see it anyway.