Happy to read your experience. It is generally admitted (and true IMO) that the Y service is usually much better on Euro airlines than on their US counterparts, but the latter have also made a lot of progress to be honest, especially DL.
The food is much better on AF without any doubt, but the 2nd meal (snack) is sometimes better on DL especially for the "short" flights to the east coast/midwest. DL is at total shame for the wine they serve in Y, in bulk bricks like milk or orange juice. I'm not saying that the AF wine in Y is great, certainly not, but is still much more decent than the vinegar served by DL.
You say that DL serves 3 meals in Y ? Unless this is something recent, I don't think they serve 3 meals on Europe-US flights. And who needs 3 meals in a 7-8 hrs period ? And if you want alcohol with your 2nd meal with AF, there is no problem, you just ask.
The "disappearance" of the FA after the maim meal service is often a reproach made to AF and it's more or less true, but there are always some FA on duty to take care of pax. You are perfectly right saying that DL FA are more proactive going through the Y cabin to distribute some water. But I have seen that also very often with AF crews, so likely a matter of better crews than others.
For me, I would always choose AF vs a US airline for a trip in Y if I have the choice.