Arthur actually played key role in his development as he showed a lot of faith in him and he was the one who promoted him as a t20 opener and 3rd in ODIs. He also took criticism from the media when Baber was failing and didn't change his position.
It is a simplistic argument that is not backed by concrete evidence. A quality player doesn’t need many excuses to succeeded or any excuses to fail. The notion that someone like Umar suffered because of batting position is not true. He is a dumb player who would have failed at any position in the long-run.
Secondly, Babar has always been a top 4 player and has never showed the hitting ability to be suitable for a lower-order role. The reason why Umar got demoted from the number 4 (where he started against Sri Lanka in 2009) was because he batted like a slogger.
Someone like Shehzad never got demoted from the opening position and neither did the likes of Jamshed. The lowest that they have ever batted is number 3. There is no evidence that Babar would have batted in the lower-order without Arthur.
He made his debut under Waqar against Zimbabwe in 2015 at the number 4 position and batted ahead of Malik and Sarfraz.
Against England in the next series, he batted in the following positions in the ODIs:
Number 6, opener, opener, number 4.
The reason why he batted at 6 in the first ODI is because Pakistan had to accommodate the departing Younis for a farewell. In the following ODIs, he opened twice and then batted at 4 when he didn’t do well as opener.
In the next series against New Zealand in January 2016, we played two ODIs and he batted at number 4 both times. He scored 62 and 83.
This was the last ODI series before Arthur took over as coach.
In the 7 ODIs that he played before Arthur, he only played down the order once (to accommodate Younis’ farewell), was actually tried as an opener and batted at number 4 otherwise.
Hence, there is zero evidence that Arthur was the one that did him a favor by batting him up the order. He wasn’t the one to come up with the idea of opening with him either, because it was tried by Waqar already and he had had been opening at junior levels throughout his career.
If people want to give excessive credit to Arthur because they have an axe to grind against Waqar and Misbah, so be it. However, the factual evidence does not support their claim.