There is no one to blame here and indeed luck was on Manchester United's side so they were able to win the match in the final minutes, I think the substitutions made by Klopp did not affect the team's performance in that match and in my opinion Liverpool's defeat was due to their bad luck and On the other hand, the Manchester United team played a little better even though they were not favorites in this match, but they managed to answer these doubts quite well.
This is a trophy that is possible for Manchester United to win this season, they are very close to the FA final this season because in the semifinals Man United will not meet a tough opponent.
I agree with you that nobody is to be blame but though most persons are feeling that the bad performance of Liverpool was as a result of the changes Klopp made, so for me I think that's far from the reason why Liverpool performance was not that consistent and besides we know how Klopp pattern has been working for the club which has lead to there numerous wining and being on the position they are now, however one thing we most also no is that after a coach has established his pattern to the players to use, it will be left for the players to effect the strategy in other to win the match, so in terms of Liverpool on that match they failed to utilize it because Manchester United did not really give them the opportunity to and it got to a point where most Liverpool player was no longer confident on themselves that's why on the first half they barely hold a ball without being intercepted by the Manchester United players.