I think Amad deserves a chance but from what iv'e observed he's another inside forward hybrid. I watched parts of the game when he played against Luton, Sunderland offered him many options in possession but the difference is in the league the initative will be on him with most opposition teams either sitting back or using a counter press. Bit of a controversial take but if Diallo did play next season I could see him offering more than Sancho does out-wide if he gets his barring's with the tempo.
In terms of profile I think United need someone with pace who will essentially attack the fullbacks. The mention about quality in reserve is one of the biggest issues, the drop from the level of the first team to the bench is too significant for this team to challenge. Antony though I think he will come good should be a player coming off the bench as opposed to a starter in this phase of his development. From my perspective the weakest area last season was the wide positions, followed closely by the striker and with the depth of the midfield, defensive cover and goalkeeper being issues but not as high in terms of detriment.