The sixth match at home to West Ham will provide a slight advantage for them who of course would prefer to be group winners rather than having to go through the playoff round to qualify for the round of 16, so it can be said that West Ham will qualify compared to Freiburg, especially in the away match they can beat Freiburg well especially in the sixth match later as home team.
Both teams actually have almost equal strength. But since the next match will be held in West Ham home, we assume West Ham gets the advantage because they will play in their own field and with more supporters at home. I don't say West Ham must qualify for the next round. I just believe they probably qualify because they ever defeated Freiburg in matchday 2 away and they also will play at home. However, no guarantee West Ham to qualify, it depends on how the match will be.
West Ham's performance has indeed decreased in the English Premier League, but here they are still better and that is also what they showed last season, where European competitions had better results than local competitions.
We can exclude the factor of EPL matches. I also think it won't bring significant impact on the Europa League matches. West Ham players must have a better motivation to win the last group match of Europa League. They almost reach knock-out phase, they have a big hope to achieve it. They must realize if they go to play-off, the chance to qualify can be smaller because they will play a team eliminated from UCL.