To me, it seems that those tunics in the pilots were anything but baggy. Gary Lockwood's was so snug, he looked like he could hardly breathe in his.The simple unisex pants-and-velour-shirt uniforms in the two TOS pilots, "The Cage" and "Where No Man Has Gone Before," looked comfortable and practical -- except that some of those shirts were so baggy, they could have posed a risk of getting fabric caught in moving machinery!Miniskirted duty uniforms for female starship personnel, however, were just impractical and silly. (And I'm saying this as a leg man!)
I completely agree with the impracticality of it. Not that we ever saw a sufficiently practical uniform except for ENT, but to me, it looks badly suited to shipboard life.
As far as the ENT uniforms, while people have been saying how practical they are because they have several small pockets, they're otherwise pretty tight-fitting (designed more to look good on camera than to be some real everyday wear item, IMO). They might start to be a real pain to wear after only a few hours.