i had some sample sets of different synguts offered by reps, most of them 1.30mm or even 1.35mm and in spite of stringing them lower than usual, all the set-ups just played awful. a full poly would have had more touch than these combos.
when i went down in gauge to 1.25 syn gut, some of them have been really playable indeed.
so, while it is true that the dominant string will be the mains, not simply everything will work in the crosses.
1.30 multis are pretty much o.k. for the crosses, i've had no bad experiences in this respect so far. of course, some of the strings performed below expectations, but that is a different story.