I agree that they should have a chance to show what they can do.
Wenger drove me mad with the way in which he would pick the same players regardless of how they had played. Once a player became one of his chosen ones, it was very hard for another player to wrestle his way in.
Nelson and Nketiah weren't really at the level needed to apply that to them--although, I definitely think Wenger killed Nelson's early season form and confidence by playing him at wingback and then not involving him at all in match day squads and denying him the 10 minute cameos that would have come with that. Maitland-Niles is a good example from last season though; he deserved a chance in midfield earlier than it came. Hopefully everything from this pre-season on is about a clean slate and playing on merit.
Anyway, talking of Nelson, saw this video of his best bits from this season ealrier:
Such an exciting talent!