And how many of those were in the late game, when he came in with fresh legs against a tired opponent? I don't want to badmouth him, but with that logic you could also have said Joselu was a high tier striker. It's always easier to score in the end as a joker, than scoring consistenly while starting.
He played 5 matches for 90 minutes this season, scored only in one of them twice at home against Leganes. Many other games he started an played 60-80 min, he didn't score as well. Look it up on Transfermarkt.
He's not bad, but certainly not great either and soon 30 years old.