I have spent the last 4 years on the internet and talking to butchers to try and find a really good, tender steak. Funnily enough I found some amazing steaks by sheer accident a year or so ago. We were at our flat in St Cyprien, Languedoc...and I did a quick shop on the day we arrived at Lidl...and found American Steaks in the freezer cabinet...expensive...at around 10 - 12 euros for two steaks, but frankly...I was missing a good tender, pink steak. It turned out to be the most fortuitous shop I had done in a while...the steak melted on the tongue...superb. Sadly they stocked them for 3 months and then no more. I found this article on line, and it explains a lot. Written by an American in the food industry who has moved to France I gather.
French beef is different to US beef in many ways. Firstly, you’re likely to be eating a culled cow of 4-10 years. That is way older than any US beef. US beef is usually under 2 years of age. In the US, culled cows make hamburger meat.
'In the US when you get a steak you will likely be getting a steer (castrated male) but in France you will get a fattened retired mother cow. The male calves in France usually go to feedlots in Italy and Spain. They are the premium product.
The word ‘boeuf’ means a steer when you say ‘un boeuf’, but you aren’t likely to be eating one in Paris unless your butcher has a special (and expensive) deal with a farmer.
US beef is also mostly feedlot beef where the young animals spend some months in a facility where they are fattened up in large numbers. France has its feedlots up north where you Parisians are. I’m not sure of the percentages but there’s less feedlot beef here than in the USA.
As you point out, a lot of beef is retired dairy cow. THe number I have read is 60%. I wouldn’t say it is lower quality offhand, since I think a Normande gives a better steak than the big three beef races (Charolais, Limousine, Blonde), but each to their own taste.
French beef will on average eat more grass than an American feedlot cow but those dairy girls could be eating fancy pellet rations and they will all be grain finished rather than grass finished. The big difference in marbling comes from the races of the cows. It would be a miracle to get a US Choice or Prime rating from a Limousine, Blonde or Charolais. They’re just not bred for it.
Your best bet for marbled beef would be the three local cows, the Salers, Aubrac and Gasconne. The Salers has the reputation of being the most marbled of the European cows. We have a herd of them down in the SW. 
As you say, talk to your butcher and they’ll know what they can get. Best of luck finding good steak!'
Which explains a lot to me about the meat. I honestly thought it was just down to not ageing it properly....obviously, France actually exports the best of its meat to Italy!