I find that not only counter to any sort of drama one would desire in a game but absurd from a believability stance. I think, as is, it reveals a real flaw in the game.
No I cant speak for the Imperium setting and all, I havent played classic traveller, but from a 2300 perspective its entirely counter to the feel of the setting. A small freighter lifting off the pad only to see an armored vehicle approach and begin shelling them with anti-tank rounds should be terrifying, and potentially disasterous, not comical.
I was answering from the rules POV, not about my opinion.
About my own opinion, it would be as terrifying as a sea ship leaving the port and seeing a tank coming firing at it. If it is a freighter, it may be in danger. A modern destroyer may also be hurt, but it may fire back. A WWII destroyer would not have been too scared from a tank gun, while the tank would be quite scared from the ship's guns.
After all, the destroyer's guns, usually in the order of 4-6", being about the smallest on warships, were heavy artillery for ground troops. The heaviest guns deployed on ground (AFAIK, and excluding naval defense batteries) were 203 mm (8")", that were "only" cruiser weaponry, and guns over 155 mm (about 6") where very rare on ground, while quite common on ships.
We're really talking about two diferent scales of weaponry, and naval fire uses to be quite devasting against ground troops, while the return fire uses to be quite ineffectual.
In 2300 there is no ground weaponry able to damage orbiting ships, and once orbital supremacy is acheved, only reinforcements can save the planet, as the ground troops have no way to respond fire. Beams (lasers and PAs) cannot be to battle planet vs ships, as long as the planet has atmosphere, space missiles are useless inside the planet's gravity well and messons and space rated high energy weapons do not exist.
In CT/MT/MgT, there are weapons able to fire against ships from ground (laser batteries, missiles, deep meson guns...) and vice versa (ortillery is specifically told about, using from lasers or missiles to high energy weapons to meson guns). In MgT there is not restrictions (at least that I've read about) for PAs to be used from/against atmosphere, so they could be added to this weaponry (and being quite lower TL and not requiring EP/Mw they will be more common).
About atmospheric/interface fighters, in 2300 they are either planes or, at most, interface planes, that could well be armed with lasers (missiles would again be out of place inside the gravity well), while in CT/MT/MgT they are gravitic spacecrafts fully armed as so. So, while in CT/MT/MgT the same fighters may be used as space, interface or atmospheric fighters, in 2300 you need a diferent craft for each role, but the ones for atmosphre/interface are not warp equiped, and so easy targets for space ships (at least from the moment they leave atmosphere and are vulnerable to their weapons, and before that, they cannot either damage the orbiting ships).
As told in other occasions, I had not the opportunity to read MgT2300, so IDK how Colin has matched those paradigms while trying to convert 2300 setting to MgT rules. To keep the 2300 setting, starship weapons must be ineffective against atmosphere, while if MgT rules have prevailed acheveing orbital supremacy is no longer having won the battle, as your ships are no longer safe from planetary fire while in orbit.
As I already told in another thread, in 2300 the only way an interface plane could reach the orbiting ships to damage them would be by having very heavy armor (as Martels have) and "a little" luck, and even so the orbiting fleet could just abort stutterwarp discharge and leave orbit while the interface ships are climbing.
All this said, from the drama POV, I agree with you all this is unfortunate.