I didn't see the weakness you saw, although I did get a shock in the first 5 minutes. 5 minutes though doesn't make a football match as Utd found out to their cost.I thought Barca looked quite weak today and beat a very poor United side.
If we beat Spurs & Ajax which is a big ask but doable I think we will play Liverpool in the final.
Barcelona are favourites for me. Unlike Man Utd, Liverpool carry a punchers chance. Mane, Salah are seriously quick and the power of Liverpool's midfield might trouble Barcelona. Not 100% convinced that Liverpool will beat Porto. Porto carried a lot of threat at Anfield and could easily have scored. If Porto score first that game could swing. Not expecting it but Porto did cause Liverpool a lot of problems at Anfield, and Liverpool's away record is not great this season in the CL.