I'm short-waisted and long-legged so untucking makes the proportions work better for me.
The other trick I have is that I have the sides of my t-shirts taken in if they need it. Things with stretch are usually okay but I like plain cotton tops to be a bit narrower at the waist than I need for my chest and hips.
If they're going to make clothes in four sizes only (S/M/L/XL) there are going to need to be a lot of alterations to make the clothes work.