West Ham United are in good form in the last few matches in their domestic league while Frankfurt are certainly now with high confidence after they were able to beat Barcelona and advance to this semifinal.
I think the match between these two teams will be very balanced and interesting and both teams have the same chance to advance to the final round of the Europa League this season.
Personally, I'm still more confident in West Ham United because clubs from the English League are always stronger and more consistent than German League clubs like Frankfurt, even though Frankfurt have beaten Barcelona.
However, if we examine in depth, Barcelona is also not as strong as in the past, so it is natural to be defeated by Frankfurt this season in the Europa League.
I think Barcelona's defeat to Frankfurt is unnatural, because from the quality of the players Barcelona is still very far ahead of Frankfurt. it was a surprise result, but that's football. anything is still possible.
In the semifinal match, West Ham United is certainly still very advantaged compared to Frankfurt, but this is a Semifinal match where every team competing here will give their best game, and in my opinion it is not impossible that surprises will happen again.
Are we still talking about Barcelona, a couple of weeks after Barcelona dropped out of this competition?

Why would the defeat of Barcelona by Frankfurt be unnatural or strange?
Frankfurt played two very good games against Barcelona and deservedly advanced to the semifinals.
I agree that the German league is in crisis, and that English clubs are better in international competitions in recent years.
West Ham is probably a serious favorite to win this competition but it was also Barcelona so we know what happened
