Reus takes the place of the Monday Ibiza, which switches from Mon/Fri to Thu/Sun
Reus wouldn't, directly at least, replace Blackpool as the sector lengths are so different. BFS-BLK is effectively utilisation flying. Unless you do a night flight, which Jet 2 generally don't do, you can't fly to Spain 3 times in a day. But you can do Spain twice and a short segment such as BLK