Hull Types no real advantage

Nope, there's no difference in hull stats. The hull techs only give you the capacity to build larger hull classes; they don't affect sizes you are already able to build. (There are a couple of hull techs that raise hitpoints of all hulls.) All the stats you mention, aside from cost, are handled by other techs and components. For example, miniaturization makes your hulls larger, not the hull techs.

The hulls you mention are just additional hull types of the tiny and small types, and the only differences are cosmetic.

...which begs the question: why aren't ALL tiny and small hulls available at once? There's no need to tie a cosmetic feature to a research tech like that.

Kid,
So why not have available at the start have all tiny and small hull types available? Makes no difference right just looks. Building large class vessl with techs I can understand. Yet in each hull type should have its advantages an disadvantages. If it is just window dressing as a weapons platform you should have all those tiny and small hulls at the start.

Some hulls should be better for missle, Gun or Beam plateforms. Then a gain using a combination of weapons based on hull type not Weapons.

My Idea as a mod
Type-cost-size-hp-speed-logistics-sensor range
Tiny1 start: tiny-35-16-6-3-3-3 increase speed,logistics and sensors
Fast Light fighter let me attem! I like reachout and touch ya!
----------------------------------------------------------------------
after Xeno Idustrial Theroy(XIT)
Tiny0 XIT : tiny-40-18-8-2-2-2
cost up, hp up, size up, but speed logistics and sensors down
Good Heavy Fighter slow but I pack a punch!
----------------------------------------------------------------------
after Advanced Hulls (AH)
Tiny2 AH : tiny-45-20-10-1-1-1,
cost,size and HP up, further reduction in speed, logistics and sensors
Heavy Bomber, take a licken and still keep on ticking, I am for the knockout punch
--------------------------------------------------------------------
The same can be done with each class and a reason to research a class

Not a bad question. From a game design perspective, I would guess it's because you have to have access to at least one of the little hulls, or you wouldn't be able to start with scout ships. As (aside from racial techs) you're starting pretty much from scratch, they don't want you to have any more than is absolutely necessary, so the other styles come with the XIT. I would assume that's also why they attached those hulls to a non-hull tech like XIT; it's always going to be researched early.

Theres no reason to hold back the hull graphics from the player. The ship designer is such a huge selling point of the game, the last thing you want to do is arbitrarily limit the player's creativity!

Like I said, that's probably why they tied it to a standard early tech like XIT. You're pretty much guaranteed to have that researched by the time you research enough other techs to even be able to start building fighters.

Even so, you have additional tiny and small hulls that are bound to advanced hulls, which is not a tech you generally get unless you're either going for medium hulls or the hp boosting trade good.