I'd love a good space game ships of all these classes each filling its own role, but I don't think that game is Elite.
Gameplay wise I think they've said they always wanted Elite ships to be about piloting, and beyond a certain size it wouldn't be. I already dislike the large ship mechanics, dogfighting with smaller ships and hitting them with their forward firing main guns. Anything bigger would be a bridge too far and would require entirely new gameplay mechanics. Maybe if they devoted a whole expansion to it, but that's not where I'd hope for them to put all those resources.
Lore-wise, do such ships even exist in the Elite universe? As I understand it the size of the mailbox is a strong limiting factor on the size of ships. Once you get bigger than that you have to ferry stuff back and forth or have a dedicated dock, which is why there's a sharp jump in size lfrom the playable ships to the vast capital ships. I don't recall coming across any mention of intermediate classes of ships - several books feature Anaconda and Cutter sized vessels along with capital ships, but nothing in between (other than the Panther Clipper which is still on the playable end of the range.
1.
I dont see how thats a Problem.
Keeping an Enemy Ship Broadside with an Frigate or Destroyer. Especially in First Person would Require a Great Deal of Piloting Skills.
It would also be something requiring a different Skillset because you have to be able to Navigate mostly by Radar and Sensors rather than on your Sight.
2.
Dogfighting should not happen for anything beyond a Corvette.
In Reality as well. Corvettes had their Weapons Forward Facing.
Starting with Frigates and Destroyers the Weapons in Reality Started Shifting towards Broadsides
Which means that these Ships would have an Completely Different Flying Style. As they would not Turn after you. But rather attempt to keep Distance in a Diagonal Stride to you. In which they can Bring their Weapons to Bear on you while Rolling the Ship to keep Firing Arcs
Which at the same time means the Corvettes should be the last Ship where Forward Facing Weapons would be a Thing.
But at the same time. Corvettes would get an entirely new Role here.
Because with their Heavy Frontal Weapons and the Ability to Mount Strong Lasers while still getting several Torpedoes and Rockets on Smaller Slots. They would be the Choice of Ship when you want to Sink an Frigate or Destroyer
Since they got the Power to get the Shields of an Frigate or Destroyer Down and then lash out Mean Torpedoes into its Hull to Cause massive Damage
3.
I cannot tell if this stuff exists Lore Wise.
I never bothered much with the Elite Verse before Dangerous.
But I dont think thats a Problem.
Since the Universe is Evolving. So New Ships and also new Ship Classes being Build would not be Surprising.
The Mail Slot is not a Problem here.
There is alot of Easy ways to other Docking Options like External Docking Bridges etc.
Moreover. Since they also Started adding Bigger Space Stations like Shipyards and so on. It might also make sense. That Frigates and Destroyers would simply not be able to Dock at normal Spaceports which only got the Mail Slot
And then there is the Fact that an Frigate could have Class 9 and Class 10 Hangar Bays.
Which would be able to Hold Ships up to Small Landing Pad Size. And thus Act as Intermediate to Dock at the Station while your Main Ship waits outside the Station
More than enough Ways