I couldn't find the stats, or was too lazy to, for the number of games started and from the bench from both players. You are implying that if Morata had more starts his goal tally would be better than Lacazette? It's true Morata doesn't get to start regularly but maybe he doesn't have enough quality to do so for clubs at that level? Also, with Juve and Real being so much superior than their opponents (bar maybe 3 clubs), isn't Morata supposed to have an advantage over Lacazette?
Average per game, or per 90 metrics, Lacazette outdoes Morata considerably in everything attack. To be fair to Morata though, he did a lot better than Lacazette in the CL but it could have something to do with the quality difference between Juve and Lyons. We each have our preferred player, which Morata happens to be that one for me weirdly. But with that many variables in comparisons and difference in league competitions and we're going to go for firepower, I'd say it's a safer bet to go with one that is already banging them in for a couple seasons.