Again, important is subjective. I retract the adding to tally point, but his goal tally is predominantly against bottom half teams or clubs fighting relegation in la Liga, barring 3 clubs. As I say, important goals need more context.
Going back to my root point though, there were other important players ahead of him for the club. And there are many other strikers better than him in the world today at a similar age.
It might be subjective but converting 1 point to 3 points shows how important those goals were.
Morata was behind Benzema in the pecking order and there isn't any debate on that, so Morata can't score against bigger clubs when he never got chance against them.
Vs Barca - Injured + Unused sub
Vs Atletico - Injured + Unused sub
Vs Sevilla - Unused sub + 0 goals (63mins)
Vs Villarreal - 1 goal (26 mins)
Vs Sociedad - 1 goal (101 mins)
Vs Bilbao - 1 goal (20 mins)
Vs Espanyol - 1 goal (89 mins)
Vs Alaves - 1 goal (23 mins)
Vs Eibar - 0 goals (45 mins)
So that's his record against big team in league (top 10). What you said has some truth in it, he wasn't played in big games but when he got chances against rest of top 10 teams he scored the goal.
Also scoring goals against midtable teams is very important, we have seen how much we struggled this season against midtable teams.
I agree with your last point, there were important players than Morata at Madrid and many better strikers than him in the world but that doesn't mean they are interested to Join ManUtd.