Yeah, each sport seems to have an amount of games where you basically reach a rough equilibrium in the standings.
This is why I think a sport like basketball (I'm not a baseball fan so I won't speak on that) actually has too many games. Nothing to with player health. Teams are just fighting over minor seeding differences for around the last 20 games. Only really matters to those fighting for the last spot. At least for me, a certain degree of fan fatigue sets in and I'm just waiting for the playoffs because not nearly enough games actually matter.
Football doesn't have near the number of games to reach that. I do love that each regular season game in football matters so much more than in other sports, but one game wouldn't take away from that. Adding an extra game would remove a little of the luck factor u mention, and get us closer to seeing the true best teams making the playoffs. But I don't think we could ever add enough games to reach the equilibrium I'm speaking of.
I don't think we'll see much change in tanking, but I think it would be a slight increase if anything. Yes, the extra game would leave some more teams in the hunt a little longer. But overall more games would be played by teams that are mathematically eliminated. Though I don't consider tanking to be a big problem in football (especially when u compare it to a sport like basketball) and it would still mostly be seen among the bottom dwellars that wouldn't be impacted by the change.
But until having an 18 week season feels like the norm, I could see eliminated teams using it as an extra excuse to play even more garbage lineups in that additional and unfamiliar week. Not like we don't see some of that in the current final week anyway. At worst, a short term issue I'm not worried about.
My only reservations go back to the combo of player health and preserving the integrity of the playoffs by having as many healthy players as possible. Without these factors I'd argue that 17 games actually still isn't enough.