Taking in account qualified numbers, only 9 punts returners averaged higher than 10 yards per return. Using guys who just barely missed the cutoff in numbers of returns, there were 11.
Total yards returned for the NFL (just punt returns) was 7,690 yards. Total number of returns was 945. Averages out to a perfect 9 yards per return, and just slightly under 2 returns per game. The Packers themselves had 20 punt returns, 1.25 per game. Highest team had 44 (3/game), lowest team had 12 (0.75/game).
Using the most extreme stats, GB averaging 5.9 yards sans Davis, and the league high qualifying returner at 14.1, for a difference of 8.2 yards. Now let's say 3 returns per game, which was the league high, and you get a total difference of 24.6 yards per game.
My guess of 16-20 was pretty close, it turns out.
You're right, that number was pretty close.
But the issue I have isn't just that the guys we have in house would create a low average punt return. It's that about half of our opponents' punts would not be returned. Williams and Cobb combined for 19 returns last year and 16 FC's. Davis had the problem of fair catching too often as well, but he was new to the role. If he improves in his judgment, the difference in field position would be more pronounced because not only would he average significantly more per return, but he would actually be creating more returns.
Take a nice round number of 50 returns.
Say the crew of underqualified guys decides to actually return 25 of them at 5.9 YPR. That's 148 PR yards on the season, or about 10 per game. But your true average, factoring fair catches, is 2.96 yds per opponent punt.
If Davis were to return 35 of them at 12 YPR, that's 420 PR yards, or 26 per game. The true average here is 8.4 yards per opponent punt.
The difference seems small, and it is on an average basis, but it wouldn't always be 8.4 yards. Sometimes it would be nothing, and sometimes it would be 20. Sometimes it would create really favorable field position. And favorable field position leads to more scoring, statically.
It's not all important, but it matters. So I don't know why we wouldn't keep a 53rd guy who can contribute in an area that matters as opposed to a healthy scratch linebacker or some OL who is roughly equivalent to the guys on the practice squad.