A details of probability to end in top 8 and top 24 of clubs in Europa League. Anderlecht, Olympiacos, Frankfurt played well and have high probabilities to finish in top 8. Some big clubs are fighting to complete group phase in top 24 and many of them nearly don't have chance to finish in top 8.
This means there are chances for unwated matches between big clubs in a next phase, after playoff matches. Manchester United despite of disappointed performances in Premier League, are playing well in UEFA Europa League this season and they almost have a position in top 8, with high probability as you can see below.
I do not know where you got that chart from, but that is not the rankings, Olympiacos is seen at 8th, when they are 12th for example, and there are some other mistakes too if you just compare it. While I understand some teams which are lower right now, could have better chances than teams that are higher, which all makes sense because if you are facing an easier team, and the other is facing a harder team, then even if you are lower then you have a higher chance.
However, I would say it would be better to keep the ranking as it is, and then give odds accordingly on the side. In the end, we are going to see how the league will shape up after the game, and I feel like finishing 7-8-9-10 have a great chance to move forward, because you are not facing big teams, you are facing teams around you, which makes better chances for all the teams, and most will achieve for that.