Yeah, end of the season seems fair. Although, Mudryck who is a similar position, same age and similar price did well on his debut - whether that is a one off or not remains to be seen I guess. It doesn’t have to take a season to get going in a new league.
I disagree I think a player ought to show glimpses at best, but accomodating to a different footballing culture, environment and tactical influence can take time. Pep has spoken very prominently about the differences of managing in England and elsewhere. Klopp has done the same. One of Grealish's recent post match interview (against Spurs) he spoke about how hard he has found adaptation to the demands and responsibilities of Peps system. It's not just about the league, it's also the team, the shape and the philosophy. We fans generalise the transition to English football but the specific team in question is important. ETH seemingly vehemently sought after Gakpo and he's looked disappointing for Liverpool but that doesn't necessarily reflect how he could have performed at United.
The issue is United are in a transition and period of change where players aren't awarded time from the fans because of the expectation that the changes need to be immediate and impactful. The lack of competitiveness over the years doesn't help, a player that requires time to develop is less of a burden in a functioning winning team compared to one trying to establish themsebles. The reality is it's an unrealistic view. There are too many factors that accommodate a players form for their to be a black and white answer.
Dalot is a great example, he showed absolutely nothing aside a few step overs and a change of pace on the right wing in the first 12 months and was absolutely awful defensively in various performances. Didn't do anything of note on loan, time passes he comes back to the latter end of Solskjaer's tenure doesn't play much. ETH comes in and he (putting it lightly) hits the ground running. Could probably even be said to be one of the best fullbacks in the prem this season on form. It's impossible to track that type of progress like a case study.
I think the fans need to have patience with certain players. The only area I can see where a player should be expected to have a faster rate of implementation into a team is when they are already purchased from the league. I think this is where Liverpool had good success with the likes of Mane, Robertson and VVD. But players coming from the Bundesliga, Eredvise, Serie A etc should be given more leeway.