Galatasaray is probobly having one of the worst seasons in their domestic league in history so far,they are really struggling to not get relegated and they are the biggest club in Turkey. This match should be an easy win for Barcelona and i can already see them in the next round of the Europe League.
Yes, the outcome seems obvious, but I won't bet here. In the end, we don't know anything about the plans of the teams and I don't see any reason why there can't be a repeat of Borussia - Rangers here. Plus, I have very little idea how Galatasaray plays this season (maybe they, like the Russian Spartak, are experiencing a big crisis inside, but they play acceptable in European competitions).
It is easy to predict that Barcelona will win, not just because Galatasaray seems like a bad team, but because Barcelona is a great team normally way above europa levels. I mean this doesn't mean that the result is guaranteed, I wouldn't go as far as that, in football anything could happen.
However, how many teams are there in europa league where you would say Barcelona will lose against? I wouldn't name more than maybe a few, definitely not more than 3, and Galatasaray obviously is not there. They are horrible in demotic league for sure, but they were first in the groups so it shows that they are not as bad as people think, but they are still not as good as Barcelona.