The farmer thing is clearly just a thoughtless insult, not totally surprising given this is a forum about a club in Spain/Catalan, but I don't think it is cool, I have decided not to use it.
I was using using both 5 year Uefa ranking and total player market value form transfermarket--the latter a good indicator of collective talent. These don't always come together, but close. La Liga has regularly cleaned up in Europa, and they are not Real or Barca, and these teams do it with Europa 2nd fiddle to league and maybe co lower club goal with Spanish cup.
Ligue 1 is solidly the 5th league in the world, I would agree. But they really only have one team with ambitions to win the champions league within the realm of possibility due to financial might, and that might comes from Qatar--not from league revenue or anything shared collectively to the clubs.
IMO
La Liga (not necc this order, EPL better in some areas like most of the bottom 1/3rd of teams)
EPL
(solid gap)
Serie A
Bundesliga
(solid gap)
Ligue 1
(solid gap)
other Europe and S. America leagues
Along with the Uefa ranking and squad/league player values--all relatively objective, you can see a lot of cases that support this. How many players get older or just can't quite cut it in Spain or England but whose productivity shoots up and cements a place in the team in Serie A, Bundesliga and Ligue 1 (Payet and Depay are great examples, also see Rami, Remy, Dubuchy). And there are many cases of players burning it up in those leagues who when moved to England or Spain become more exposed in terms of the limitations. Now I can't think of great players who moved from EPL or Spain or Italy but then struggle in France--certainly not Neymar, Cavani, ADM.
I think you're wrong with that "solid gap" between Serie A/Bundesliga and France. First of all because Bundesliga is a better league than Serie A (watch some games in both league to make up your mind about it, or just wait next season or the one after to see Germany take 3rd place in UEFA rankings). Second of all because the gap is not that big.
You're mentionning "great players" who moved from other countries to France and then didn't struggle. That's necessarily biased for one good reason: French teams have less money than other teams in general. How is Bordeaux going to buy a "great player" ? Therefore, most "great players" are bought by PSG, who are already a notch above everyone else. Helps not to struggle.
Second of all: you can't reason by listing examples. If you want to talk about players going from other leagues to France, what about Strootman, who's pure shit with Marseille ? What about Grzegorz "La Liga team of the year" Krychowiak who ended up as one of PSG's biggest flop ? He's actually a perfect counter example: he was ok in France (nothing super fancy though), went to La Liga and instantly turned into one of your best MD. Then he went back to France, and he was shit again. Can also mention Cabaye, who at the time was linked to United and other big teams but joined PSG... and failed terribly.
Those are just two counter examples, but even your examples are not all good (besides the PSG ones, though any PSG fan can tell you how fed up he is with ADM who's never been that amazing there). Payet had turned into shit (his best season was in West Ham, not in Marseille), so has Rami who's just a joke now. Debuchy is good since he's back in Saint-Etienne, but he wasn't bad in Arsenal, just injured all the time. Depay was great last year, but his first half season was meh, and he's only scored 5 goals this season, so not like he's crushing it big time, but I'll grant you this one.
On the other hand, I can name dozens of players who were good in France but shone even more brightly in another country. Lenglet for example played for NANCY (of all teams !) in France. He looked rather promising, but nobody could have guessed he'd end up in Barcelona 3 years later after two great seasons in La Liga. Already mentioned Krychowiak, but he's a perfect example. Kante was good in Ligue 1 and everybody was a bit surprised when he joined Leicester because people would have seen him in Marseille or Lyon for example, but again: nobody expected him to be such a monster so soon. Alassane Plea is having a blast in Bundesliga, so did Anthony Modeste before him. Lille couldn't wait to get rid of Pavard. I could go on for hours.