Nketiah should have come on rather than Laca. Not because the latter didn't do well but because he should have bigger battles to fight.
Another few minutes, another goal in a short time - that's exactly fighting the bigger battle by keeping up the momentum of your striker and his confidence to score whenever he's on the pitch, even if only a few minutes.
Would have been nice for Nketiah to get a stroll out, but down the line having Lacazette firing and up on confidence is much more important than handing out a few minutes to a youngster. Especially in the situation we're in - fighting to get back into the top 4. Nketiah won't make any difference in this, but Laca's form will.