Everyone seems to be missing what for me is the most important piece of space combat: stealth and detection. To shoot at things you need to be able to detect them.
Screening ships will be far more about extending the eyes of the fleet and less about fighting.
ECM and ECCM should be very important capabilities here.
It depends how the designers want
Traveller space-combat to look and feel.
In a "realistic" style or feel, there is no stealth in open space/vacuum without some sort of super-science that is otherwise unspecified in
Traveller. Every vessel would be radiating heat well above room temperature (>300+ Kelvin) in infra-red (due to life-support & power generation systems) against a 2.7 Kelvin microwave background with nothing to hide behind or absorb/attenuate the IR-signal - every ship would be a giant glowing IR-lightbulb against the blackness.
But
Traveller has always dealt with "detection ranges" historically, which at least suggests that some type of unspecified signal damping or scattering must exist at some level if ships need to first detect each other in open space. In fact, the absence of any provision for "heat radiators" in starship design implies that something is dealing with excess heat in some way (otherwise the crew would cook). One hand-wave is that it is some type of spin-off benefit of the M-Drive or gravitics in general that is spreading/damping the heat/signal out to other bodies in the star system.
T5.10 Book 2 ACS Starship construction does include Stealth-mask as a starship defensive system vs. active sensors (which specifically includes ECM & ECCM per the text). It may be that the issue is less about
detecting the presence of targets as much as being able to accurately
resolve them for targeting purposes.
If a super-stealthy missile with a hydrogen bomb warhead penetrated close enough, that would surely be a kill. The Traveller assumption has been that this cannot happen in space. I’m not so sure of that. A combination of stealth, tactics and sheer mass should be able to overwhelm any warship.
Keep in mind that there will be no fluid medium (i.e. "atmosphere") to transmit any concussive force. A "Nuclear" Device (Fission, Fusion, or even Antimatter) would be entirely heat, radiation and/or EMP damage unless it were VERY close.
BTW, don't get me wrong on any of this. I rather like all of the tropes you mention above as well. It is just a matter of how "realisitic" or "space-opera" you want to be (or in this case, what do the game designers want it to be). I have always come at
Traveller as "Hard Space Opera" (i.e. somewhere in between).