See your point, however, the squad is big enough to compete in several competitions at least for now. I do not see us winning the FA cup to be honest, whereas top 4 will not be an easy walk either as Chelsea are likely to improve under Tuchel and Klopp will get his team back on track sooner rather than later. EL is basically a trophy and a 100% guarantee of Champions League football next season. I would definitely have it as a top priority.
I’d definitely place it above the FA Cup in terms of priority as well because like you say, it’s more than a trophy - it’s a trophy and 4th place in one.
But I think a basic principle at United is to compete for every trophy within our grasp. Seeing competitions as beneath us is something reserved for fans I think - a professional player wants to win anything and everything they can get their hands on. And our players need to practice the mindset required to do that.
Also there’s a practical element to taking tonight seriously and playing a strong team - if we blow Sociedad out of the water it means we can rest key players next week in the reverse leg before the Chelsea game.
Chelsea, conversely, have to play Atletico midweek in Romania; a physically gruelling experience regardless of the result.
If we rest players tonight and then have to overturn a result next week Ole will undoubtedly have to play our strongest XI and it will be a slog - 3 days before we play Chelsea.