Sevilla's squad is not bad. But since the start of the season, we have seen poor performances from Sevilla. The team is not playing well. Their overall performance is poor especially due to their poor match strategy. At the same time, I will say that Sevilla's forward performance is very poor. The forward players are not able to play well so Sevilla is not playing well against relatively weak opponents. At the moment, Manchester United is a very big opponent for Sevilla. My guess is that unless Manchester United makes a big mistake, it will not be a difficult task for United to beat Sevilla.
The bottom line is that what Seville has at the moment means the worst and it is true. Sevilla cannot compete at the top and that proves how weak their capacity is in the domestic league. But in the European league competition they got very good results to advance to the quarterfinals and will face Manchester United later. But the mistakes like you said are unlikely to happen, considering that Manchester United can be relied on more to win in this round against Sevilla.
The situation of the Sevilla team is currently very poor. The team has been able to perform well in some matches. The team has some players who are giving their best game for the team, resulting in a great performance in Sevilla's attack. The position of the party is currently relatively stable.