Morata has scored 18 goals in 34 competitive caps, it is very much decent. 9 of the games he wasn't starting, either. For a comparison, Torres scored 28 in 65 games.
Since that u21 tournament he played with Thiago, I always saw him as a natural goal scorer, but he seems to be on a 10 year draugt of sorts, maybe I'll soon have to adjust my view of him... He runs intelligently, is decent overall, arrives at a lot of chances, but maybe fails to convert too much, but he is still statistically very much a good goal scorer. These are his goal/90 ratios in different competitions:
Champions League: 0,58 (3558 minutes)
La liga: 0,7 (5540)
Premier League: 0,48 (3002)
Serie A: 0,46 (6015)
You won't find that many attackers with a better track record than that, and the ones you find will be tough to get to Barcelona. But I of course prefer Cavani, his track record is better too.