Yes, it's a stretch. I have not flown SQ long-haul in Y, but I can say confidently that any business class is better than any economy, all else equal.

The only caveat is cost -- i.e., if they are not equal. I suppose, if the fares are the same, then it depends how else you might use your SWUs over the course of the year. If you run out of SWUs and have to take UA trans-Pacific later, for example, then of course better to suck it up on SQ Y now.