Most times French clubs are seemingly difficult to face especially in this kind of situations, just like what Monaco did against Barcelona in their first game of the Champions League this season, but if Leverkusen can stay focused then they can also beat FC Brest too, perhaps they have faced a more stronger opponent like Milan so Brest shouldn't be much of a challenge considering the quality of players available in the Leverkusen side, I totally agree with you that they have all it take to go far this season in the Champions league and probably achieve something big.
French clubs are difficult to defeat, but they don’t usually make it at the end despite the effort they put in, to me they lack some Champions league experience which we have seen several times from the top team in the League 1 which is PSG. PSG has disappointed people several times in the Champions League, they do have all it will take to win the game, but they do always disappoint at the end which has made me to stop believing in them because even the time they have Messi, Neymar, Mbappe and a lots of big players in their squad, they couldn’t win the Champions league which means they can’t win it anytime soon.
The game between Leverkusen and Brest will be a hard game to predict I must say, because both of the teams are not well experienced when it comes to Champions League and both of the teams are in good form because they both won their first two Champions League games.
My prediction will be a draw because Brest will be plying at home and Leverkusen is not too good away from home and if we consider their last match result, we can see how they played a draw against a bottom team after leading from 2-0.