Based on the players that last on rosters, elevating a draft grade because a team did a good job drafting in the later rounds doesn't make a lot of sense. There is a reason the vast majority of long-term NFL players are drafted in the top 100-150 players.
Here is how you should grade a draft:
1st round pick – should account for about 45% of a draft grade
2nd round pick – should account for about 20% of a draft grade
3rd round pick – should account for about 15% of a draft grade
4th round pick – should account for about 8% of a draft grade
So, 88% of whatever draft grade you give a team should come from the first 4 rounds of the draft. There is just a low, low probability of any players drafted in rounds 5-7 make an impact on your team. Don't beliieve me? Just look at the current starting lineup and key backups of the Cowboys team
QB – 4th round pick (Prescott)
RB – 1st round pick (Elliott) & 4th round pick (Pollard)
TE – Two (2) 4th round picks (Shultz, Ferguson)
WR – 1st round pick (Lamb), 2nd round pick (Washington) and two (2) 3rd round picks (Gallup, Tolbert)
OL – Three (3) 1st round picks (Smith, Smith, Martin), 3rd round pick (McGovern), two (2) 4th round picks (Biadasz, Ball), Undrafted (Steele)
DE – 1st round pick (Fowler), two (2) 2nd round picks (Lawrence, Williams), two (2) 3rd round picks (Basham, Gholston), two (2) 4th round picks (Watkins, Armstrong)
DT – 2nd round pick (Hill), two (2) 3rd round picks (Gallimore, Odighizuwa), 4th round pick (Urban)
LB – Two (2) 1st round picks (Van der Esch, Parsons), 4th round pick (Cox), 5th round (Clark)
CB – Two (2) 2nd round picks (Diggs, Joseph), 3rd round pick (Lewis), 6th round pick (Brown)
S – 1st round pick (Hooker), 6th round pick (Wilson), 7th round pick (Kearse)
9 – 1st round picks
6 – 2nd round picks
8 – 3rd round picks
10 – 4th round picks
So, picks from the top 4 rounds account for 33 of the starters and key backups. Only 5 key starters or backups come from the later rounds or undrafted ranks. Face it. Rounds 5-7 are for tackling dummies to assist during practice, provide emergency injury support when needed, and play special teams.
So, when you are grading the draft, make sure not to give too much weight to the 5 players the Cowboys selected in rounds 5 & 6 this past month.