Fair enough, going by your post you have a huge hardon for Morata and rate him very highly so let's discuss bit by bit.
If he's not being put in XI out of favoritism of Benzema at Real, what was the reason for not being able to break into Juve's XI ahead of Llorente and Manduzkic? Don't tell me you believe he wasn't able to break into the side because of uncertainty about his future
He did get ahead of llorente towards the end of the season, starting the CL semis and final while llorente sat on the bench. In his second season, Mandzukic was better than him and he did have issues off the pitch whether you accept it or not.
No matter how you dress it, his goal scoring record is not special. Especially when you think of the figures being thrown around for him. €90 million is a steep price tag which you pay for a special player, Morata is far from one, he is a forward who is known for his 'all-round game' rather than his goalscoring. We are a side who is badly struggling for goals and he's being bought to replace Ibrahimovic goals who scored 28 for us. Do you honestly believe he's going to match never mind better that number? Because that's the kind of goalscorer we need in the side and Morata hasn't shown anything in his career so far which suggests he is a clinical striker. In all the teams he has played for, he has never been THE goalscorer, he is always supplementary to the other forward. Tevez in his first season, Dybala the following season. Ditto at Madrid.
Never said he was worth €90m, but that does not mean one should belittle his abilities. He is fully capable of scoring 20+ goals consistently for any quality side, and has the potential to develop into a WC. The fact that you think he was supplemental to Tevez and Dybala showed you didnt see much of him at Juve.
Situation at United would be completely different, he'll bE seen as the main man who has to deliver the goods on a weekly basis. Also, we are not as good as Real/Juve in attack so he's not going to have great service he's enjoyed this season. Pogba who enjoyed first team football at Juventus for four years has struggled to meet the expectations during his debut season because of the price tag and his role in the team handed him the responsibility of being our main man in midfield. Morata will be no different, he'll have to go from being a supplementary player in the attack to the focal point.
Majority of his starts has come playing with other team B players and he has done well enough to convince. Even a player like Griezmann is not guaranteed to succeed at a new club,so tere is always an element of risk. But of all the players available, he is the best of the lot.
I don't know where to even begin on last point, James is a number 10 who has also played a lot of games out wide and yet he has a better goalscoring record than an out and out CF in Morata. James has also been bit part player for last 2 seasons. This season he's scored 11 goals and got 13 assists in 1824 minutes. Last season he scored 10 goals and got 8 assists in 1858 minutes. This is also while playing in a system which doesn't have a #10 meaning he has to play as part of midfield 3 or out wide and yet he has better numbers than a number 9 in Morata.
James is the older and better player but his numbers are not better than Morata. Morata has 1.01 goals + 0.27 assists per 90 min while James has 0.61 goal +0.46 assists per 90mins.
Don't know what development and what 'evidence' you're talking about because his stats are consistently average and far from suggests he is a highly talented goalscoring forward that this team needs. Also, it's blasphemous that you think he's the best striker on the market considering there is highly probability of Mbappe, Lukaku, Belotti, Lacazette and Aubameyang moving this summer. Every single one of them is a better forward than Morata.
If you feel having the second highest (behind Messi) goal rate per min is average, then I wish you good luck find anything better than average.
Aubameyang is older, and is not much better than Morata (if at all), and Mbappe has shown great potential but is yet to be seen if his progress will continue, but Morata is better than the lot of Lukaku, Lacazette and Belotti. The fact that the club seem to priotize him ahead of these alternatives supports my point.