I'm no tactical/strategic whiz but here's my two cents:
There are several factors that you must keep in mind when considering the advantages of all hull types. Tiny and Small hulls may initially seem superfluous but they most definately have their advantages. It all depends on your combat and design philosophies.
Firstly, logistics is the most important factor in determining how many ships you can put together to form a fleet; the hull size is commensurate with the logistics cost. You can fit in more Tiny ships in a single fleet group than you can with Medium ships. Since your logistics is going to be quite low in the begining stages of your game, this will have an impact on your projection of power.
Secondly, there's the financial consideration. Small and Tiny ships don't take as much time to build and are far cheaper to maintain than Medium ships. This means that you can build up a fleet presence quickly and project that power with faster reaction times.
Then there's the quantity versus quality arguement. Building a powerful ship-of-the-line is a valid strategy and has the potential to increase your chances of winning a battle. But it is also a very expensive investment and losing one, like it or not, will have an impact on your economy and overall strategy in some form or another. Or if you're lucky and it survives but is heavily damaged, it'll be out of commission for a little bit while it's docked for repairs. That's a piece of hardware that isn't being utilized and is a further drain on your economy. Maybe you want to group up your Medium ships into a fleet. Still...that gets expensive in the initial states of the game. Or you could build a bunch of little flying guns on the cheap and very quickly. You can group more of them into a fleet and you can overwhelm the enemy with superior numbers. You'll lose a few and that fleet's combat capabilities would have been decreased...but you still have a military presence, diminished as it may be.
Now you might say to yourself, "But I can have HUGE Hulls now. And they will seriously rock the pwn." True. They will. But by that time, Tiny and Small hulls would have been made more flexible because if you would've followed up on your miniaturization technologies, your Tiny and Small hulls will have as many as or more available hardpoints as your medium hulls at the very begining of the game. So again, you can have a Huge warship and it'll stand toe-to-toe with whatever the enemy has and brawl it out, but then there's still the consideration of time and resources invested into building that thing as well as the maintenence to keep it running.
To use a weird analogy, the Germans had superior tanks back in World War II. They were the pinnacle of combat technology back then and when going one-on-one against an American tank, the German tank would win every time. What made the difference for the American army was that although their tanks were inferior, they were cheaper to build and could be mass-produced. So despite all the technological sophistication and sheer combat power of the German tanks, the Americans were able to win through strength in raw numbers. It's something you might want to consider.