You touch on something very interesting phavoc - something I'm trying to work out with Matt now actually.
PTB say, for example, "the only turrets available are pulse, beam and missile" and "meson is only available as spinal".
However, vehicle/heavy weaponry can be mounted on craft. They also have many-km range, so... now they're back in?
What's really interesting is T5 actually does something very similar. Saying for example:
Small craft can't use turrets or barbettes. They have firm points.
Firmpoints are basically massively nerfed-range turrets (pulse and laser and missile only).
But, t5 also says any gunmaker (created) weapon under 1 ton can be mounted on a firmpoint.
Therefore, you will see fusion and even particle weaponry on smallcraft in T5!!
So like your vehicle meson example... I find it a bit silly to say "you can't mount Mesons except as Spinals" but there there clear examples of vehicle Mesons, and there are clear rules on mounting vehicle weapons
Very big lapse in logic in my opinion