I don't think Luke is really as bad as people make out. I admit he's not up to the same standard as Matt, Beth, and Gareth (when he's well), but I don't think it was such a travesty for him to be in the semis, he was better than Samia, after all.
It's a shame Gareth couldn't make the finals, but it's not like Luke knocked him out, it was purely medical, and I for one, would rather watch Luke in the final, than have Gareth risk his health when it could be something serious.
Perhaps if Oona had a stronger fanbase, she could be here instead of Luke, but other than her, I really can't think of anyone this series who should be there instead