This season, Manchester United performed better than Chelsea, but if you measure it with their performance last season, Manchester United certainly experienced a slight decline in their performance. I agree with you that Erik Ten Hag should not be fired early because the work done by Erik Ten Hag so far is still quite good because it has succeeded in bringing Manchester United back close to the top 4. Manchester United players at the start of season were also hit by a storm of injuries which hampered their game development a bit.
The busy schedule and many injured players mean that Manchester United sometimes doesn't perform better and Manchester United management must think carefully about this in order to improve again in the January transfer window. Manchester United needs to bring in lots of players to strengthen their defense sector and also strengthen their front line.
Erik Ten Hak should look for Wing Back and Center Backs to be able to bring Manchester United back into competition in the top three. The injury condition of several defenders makes it difficult for him to place players in that position, just look at how Manchester United have conceded goals in all competitions to date. When compared with Chelsea, it may be true that Manchester United's position still looks a little better, but when compared with Tottenham and Liverpool, Manchester United's position is probably far below them for now.
Manchester United has players in the front line and in the midfield position, the composition of players in these positions is slightly better and more evenly distributed. In my opinion, what needs to be strengthened is the defenders because they have a busy match, so fatigue and injuries to some players can have a bad effect on the match. This condition is what Erik Ten Hak needs to take advantage of and they don't need to buy many players in other positions for the next transfer market.