I know it doesn't really address the whole of your point but if you're determined to do combat in a small ship, it's probably best to make sure it's a Vulture.
Overall, though, small ships in ED are kind of like TIE fighters; they're just cannon-fodder for bigger ships.
It'd be nice if FDev could come up with some gameplay specifically limited to small-ships.
No criticism to your post, rather emphasizing what you write:
Why should the it be "Vulture or bust"? Why shouldn't the other ones not also be viable?
Why are small ships just cannon-fodder? When they at the same time are what new players are forced to use? I know there's plenty of people here who go like "but you have your Anaconda faster than you can sneeze", but that's for US. Who know things. And for those who look into get-money-fast schemes before even starting a game.
It's not what the usual, average new player experiences. It's those which the game is bleeding away before they even make it out of their Sidewinder. Despite some people here claiming that the game is soooo easy, the stats look different. On the PS4 you can find out how many gave up before switching away from the Sidewinder. Those people paid money for the game, then gave up on it. So anybody who claims that the game is not hard for beginners: yes, you are absoultely leet, we get it. But there are others, who are not. And they could also be paying customers. It would really be good for the game to have those, still playing, still paying random stuff from the item store, etc.
And last not least: it would be absolutely AWESOME if we would have gameplay which is made specifically for small ships. But up to now, we have nothing like that. And it's really hard to create it, too.
I mean, combat with tight areas: why bring a small ship, when a big ship with a SLF can also do it?
Blockade runner? All ships have the same speed in supercruise. So the difference would be in regular space. Where the 7.5 km would be all the difference probably. But hey, to make things accessible for those who most likely fly new ships (hint: beginners are locked into them before they made some money) the NPCs would have to be balanced around non-engineered ships. Which again means that an engineered Cutter or Clipper or even some other medium and large ships would be fast enough to also do it. So again, no incentive for the small ship.
It unfortunately is much easier to show why things would not work out, than to come up with an idea which would indeed give small ships an actual use in the game, which is not combat related.
There are also still compelling reasons to use the ships in the game, even as a part of gameplay progression for some, and a bit of fun for others. They don't need to own at combat in the game other than being a pest, and probably shouldn't anyway.
I am currently aware of only one activity in the game, where a small ship is of an advantage. And you don't even USE the ship in that scenario: when collecting blueprints at guardian sites, a small ship with a PD on top (so only small ships with top mounted utility slot count) can provide cover fire while you are in your SRV.
For anything else, be it missions, cargo transport, exploration, combat, etc. a small ship is an inferior choice. And i consider that wrong. I mean i get it, i am an oddity here. It's a collision of philosophy here. Some people believe that in games the player should matter and that different options and playstyles should be valid. Other people think that grind (followed by some more grind) should be the way to power and success.
The second point of view is what the game also expresses. First grind for money (or use the flavor of the month get money quick scheme), then grind for engineer access and engineer materials. I personally would prefer if the game would be designed to be fun at all stages and all ships being useful. No stepping stones, no waste of developer work, but everything being valuable content. But people like me seem to be a tiny minority these days.