I love the "but it breaks up the blue!" argument. Yeah, that's totally how design works. It's why Flash has trunks, right? To break up all that red? Wait, what do you mean Flash doesn't have trunks? I thought people called his costume one of the greatest designs ever put into this medium? If we need trunks to break up that red, how can this be?
That's not how art functions people. We don't 'need' the trunks from an art perspective, you're all just so accustomed to them everything else seems off to you. But from a pure design standpoint they're not needed to 'break up' anything. A good, wide belt is more than enough to do the job, if it needs to be done at all.
I can take or leave the trunks, as long as the suit looks good and works within the story I'm game for whatever. But I'd rather not have them, if I get a choice. Nothing against the trunks but for this particular character and the particular complaints that get leveled at him (often unfairly) I think it's probably best to lean into more modern design aesthetics and ditch the outside underwear. No reason to give idiot casuals another reason to whine about how 'old fashioned' and 'out dated' Superman is. But whether the trunks are there or not, it won't make any difference in the actual quality of the movie and that's the only thing that truly matters.
Personally I'd like the Reborn suit. Best update to the classic suit Clark has ever seen. I love a lot of the alt-costumes; Morrison's t-shirt non-costume, the Justice Lord Superman, Michael Turner's weird, too-busy design....lot of cool original stuff out there, but for updating the classic you can't beat Reborn.