This is a good development from Manchester United. Marcus Rashford to me has been static, he has refused to develop and it's right for Manchester united to cash in on him. Ruben Amorim has to be ruthless with his players,if he wants to achieve success at the club, and he must sell underperforming players that receives huge wages to be able to free space and generate funds to buy players that will align with his vision.
In this context I agreed with you if the best thing Amorim did was find all the advantages possessed by Rashford, instead of Amorim selling it which might make Manchester United regret if other clubs he could show its best form.
Not Rashford is actually what needs to be considered to be released by Manchester United, but Onana and Antony. Of these two players can save the cost of club expenses.
For the front lines, Hojlund, Zirczee can be used well. Releasing the two players that I mentioned can be used as an option to find a new attacker.