They're not great but they're not the travesty you're making them out to be. The problem is every team that's used them have terrible designs for their programs/associations.
I agreeI don't understand how anyone would enjoy playing in them? I play pick-up quite a bit and have never played against anyone with an Under Armor tight t-shirt. It's always either a baggy or loose tee or a cut off.
They just look stupid and I can't imagine the players enjoying them. It would feel like it was restricting your jumper.
You'll probably felt the same way about baggy shorts back in the day. I see a lot of college kids where shirts under their uniform and it doesn't hinder them.