^^ True enough. But if I made such dramatic changes then the ships wouldn't look much like the TAS versions. Believe me I did reams of sketches trying it that way and while some of it looked quite good they also didn't evoke the original designs.
I rationalize it this way. The Federation has different agencies designing, developing and building starships and spacecraft. They won't all arrive at this same conclusions particularly if the perspectives of different races are involved. It's actually like that in the real world. And so Starfleet could contract out what it needs to whoever gives them the best solution for their money, although not necessarily a perfect solution.
My backstory for the scoutship is that it's actually a Vulcan designed vehicle adapted to Starfleet's requirements. Hence the large viewport and prominent bow (which is distinctly tempered in comparison to the original TAS version).