Right, Manchester United lack option on attacking line position and make Marcus Rashford keep comfortable zone indeed has inconsistency performance in this season. Always get regular position behind how poor his statistic performance with Manchester United in this season by scoring 7 goals of 31 appearances in Premier League matches.
I think not only with Rashford but also Manchester United attacking line Antony seems overate player spending high transfer fees but get underperformance with Manchester United.
For next season, Manchester United have to find high intention competition each position how to make any players keep comfortable with their position indeed underperform.
Apart from the attack line, Manchester United also has weaknesses in the defense line if you check the standings you will see that the number of conceded is higher than scored and it is the worst record compared to the other 8 teams. Indeed, this season Manchester United experienced several internal problems such as injuries and several cases which impacts their performance. Next season is the right time to improve the team it's just that we don't know whether the owner is willing to provide a budget because last season they spent a lot of money but the results were not optimal. I think in order to be able to compete with other teams next season the owner must prepare funds of at least 300-500 million.
I agree with you, Manchester United's goal productivity this season, especially in 35 matches, is not much more than Brentford and Bournemouth. The three teams have both scored 52 goals, only Brentford and Bournemouth have played 36 matches while Manchester United have played 35 matches. Manchester United's defense is of course still better than Tottenham, Newcastle and Chelsea, but these three team have higher goal productivity.
Manchester United's goals per game ratio is 1.48 goals per game, but the goals conceded per game ratio is slightly higher at 1.57 goals per game. If Manchester United wants to compete in the top four, then of course they need to improve the quality of their defense and the productivity of their attackers. Both things are equally important, but it is still better not to score many goals while having a strong defense.