If something is screwed up with the food, they would first probably wonder why this American tourist thinks that the French chef screwed up the dish that their grandmother probably taught them how to cook. Then they'll listen to you, shrug, and take it back and tell the manager or the chef. One of them would decide what was appropriate.
If you told them you just didn't enjoy the dish and you wanted another one, they may ask you why you ordered the first dish in the first place, and why you think you deserve a free dish. If you ask for substitutions, they'd probably tell you no, because most chefs don't want to deal with that and often the way dishes are made preclude substitutions, not to mention backing up other orders. And they'd be in the right. It's kind of stunning sometimes how privileged American consumers can act.
A caveat to this is if you're in Paris; they can be really nice or really rude based on a number of factors. In a small town, French people are really friendly and helpful.
The customer is always right attitude is one that I appreciate Americans having. While not as bad in Australia as some parts of Europe, the attitude here is definitely closer to "give me your money and and leave" than "what can I do to ensure you leave happy?"
I don't need to be coddled, it's actually rather condescending.
I much prefer the European way of letting you look for yourself and then asking simply "can I help you?", if you look like you don't quite know what you're looking for. And if you tell them "I'm just browsing", they'll leave you alone, to browse in peace. Much less stressful.
There is no change in the amount of time between your order and the food arriving but that's because it's dependent on the chef/how busy the restaurant is/etc.
You can gind reports on water quality in all cities and there was an article in 2017 (in 30 millions de consommateurs?) available online where you could check any city.