Because vs. due to with adjectives?

Solution 1:

Long ago, the principle used to be that due to is adjectival, and owing to is adverbial.

In OP's example, "due to" adverbially modifies "We find", so strictly speaking (long ago) it wouldn't have been acceptable. OP would have to rephrase along the lines of...

Our conclusion that X is better than Y in most cases is due to lack of support for Y.

...which "correctly" makes a noun (our conclusion) the object of due to.

By the same principle, some might say because of is also adverbial, and that you should say "I am weak because of hunger", rather than "My weakness is because of hunger". I'm not one of those.

In practice due to, owing to, and because of are now used interchangeably. Only a few die-hard pedants maintain that adjectival/adverbial distinction today.

Solution 2:

FumbleFingers provides an excellent answer to your specific question about because of and due to.

However, this sentence has larger problems which that answer does not address.

1. It's not clear what clause (not noun or verb) due to &c modifies—is it We find or X is better than Y or X is better than Y in most cases?
2. It's not clear what clause in most cases modifies—is it We find or X is better than Y? The comma seems to preclude its modifying anything that follows; but it's quite possible that the author meant it to modify either due to lack of support for Y or even just lack of support for Y.

So it might mean a great number of things:

• We find that X is in most cases better than Y. We attribute this superiority to a general lack of support for Y; if Y were better supported, there would have been more cases where Y is better than X.
• We find that X is in most cases better than Y. We attribute this superiority to a lack of support for Y in those specific cases; wherever Y is even modestly supported Y is clearly better than X.
• We find that X is in most cases better than Y. We attribute this finding to a general lack of support for Y; our methodology assumed Y would be better supported, so our finding may not be valid.
• We find that X is better than Y. In most cases this was clearly attributable to a lack of support for Y; but in other cases Y was adequately supported and X was still superior.
• In most cases we find that X is better than Y, and in these cases we attribute this superiority to a lack of support for Y. In the remaining cases, however, Y is just as poorly supported, and yet Y is clearly better than X; we are at a loss to explain this.

And so forth and so on—I'll let you work out all the permutations.

It's a very slovenly sentence. The old practice which FumbleFingers describes might have resolved some of these issues, but not all of them.