Brest finished last year in a very good position, but we don't know if this year will be like last year. If you remember, Olympique Lyon was in last place in the first half of the league last year and was in danger of relegation. They made a tremendous breakthrough in the second half of the season. I don't know if Brest will experience a similar situation, but my expectation from them is not to be relegated but to achieve a place in the European Cups. I think their squad is a good squad for the French league. As for Paris Saint-Germain, I don't see a team that can beat them. Maybe Monaco can give them a little trouble, but Brest doesn't seem to have much of a chance.
True, Lyon managed to rise in the second half of last season, after being active in the January transfer market, so that at the end of the season they were able to finish in 6th place in the standings with 53 points. Currently, the cycle seems to be repeating itself, although they have also recruited several new players yesterday, it could also be that Lyon has a tradition of being late to heat up.
Regarding Brest, the challenge they face is actually more difficult than Lyon, where they will play in the Champions League while having to create a turning point in Ligue 1 performance. Eric Roy as manager must wisely manage the team priority scale, which in my opinion is better focused on Ligue 1.
Talking about the competition for trophies, I agree with you about PSG, the pressure that Luis Enrique squad might receive is only temporary, even if it comes from Monaco, Marseille and others. Not to underestimate any contestant, but we can easily see the gap as a fact, based on the market value of the players owned by each contestant.