Is there any fat loss benefit to cardio that would not be achieved by just eating less?

You answered your own question. It's the obvious health benefits. If we ignore the benefits then there are none.

For the specific task of burning fat though it's technically easier to avoid the 300 cal instead of burning them through cardio because you have to burn through your glycogen stores in your muscles before they start metabolizing fats. That means that you have to work for a while before you even start to touch your fat reserves. However, you can always do your cardio while fasting (while your glycogen stores are already depleted) to circumvent that problem.

The best combination of cardio and diet for fat burning depends entirely on your current condition and goals--but it is almost always a combination for best results (see obvious health benefits).

/r/Fitness Thread