I don't want to offend the two teams but a final between Frankfurt and West Ham is not what I imagine a UCL final to be.
The final match won't be Frankfurt vs West Ham, please check again the final match between Frankfurt vs Rangers.
However, I agree that it is not the expected team to be in the final. There are many top teams joining this competition such as Barcelona, Dortmund, Napoli, and Sevilla. These teams actually more deserve to be in the final round. But it is not about which team that have a bigger squad or bigger reputation, only the team that can play more solid that can qualify for the final.
Anyway, they both gave the best performances and they deserved it.
Both Frankfurt and Rangers deserve to reach the final round. They have eliminated some strong teams, they also can play consistently until the last round. They absolutely deserve as the finalists this season.
It's a shame that other big teams (like Barca) didn't make it.
Don't blame Barcelona or other big teams. There should be a chance for an unexpected result. It is a competition, the big name of a club cannot guarantee a good game.