Very rarely does a concept sketch look very much like the final product. You're trying new ideas and sometimes still tied to some old ideas until you really start fleshing things out.
For example I've always disliked the Deadelus
-class design because it looks so much like one of Jefferies' early concepts for the Enterprise
yet without adding anything to it. I see it as lazy work. I think something decent could have made of the concept, but they just didn't bother from what I see. They just hashed something out.
I look at Jefferies' early concept for the TOS shuttlecraft as interesting, but it's not finished. To my eye it just looks too wide and some of it doesn't work well. I do think something could be made from it, but I see it as a starting point and not a finished design.
I see the TAS designs in much the same way. They were quickly hashed out and little thought seems to have really been put into them. And so as has been suggested upthread I look at the TAS designs as concepts or rough sketches that need to be fleshed out and massaged into something more credible and coherent.