Tech levels

I think I fall in the school that most technology should be available for less
or more advanced groups, but its mass would be more for
low-tech groups and less for high-tech.

Take Basic example of a class 2 beam:

"Standard" Tech : Mass 2 (3 arcs) + 1/3arcs
"Low" Tech: 2 x Mass
"High" Tech: 1/2 x Mass (round up)

(Gradations between or beyond these are also possible depending how simple you
want it)

All systems (including hull and armor) are subject to tech level multipliers,
and depending on your desired complexity, you could allow progression in
different areas at different rates (as in Brendan's
Construction/Energy/Kinetic/Power divisions)

Point costs would have to be adjusted somewhat, since, for example, a High
tech ship of a given size loaded with more weapons is not linearly scaled in
combat effectiveness with a Standard tech ship with the same weapons load.

The increased mass of systems for low tech groups would make things like
class 3 beams and Screen-2 prohibitively expensive for low tech groups,
so they would not have to be forbidden outright. Technological progress would
be marked in levels of construction efficiency. Progressing from say 2xMass to
1xMass to 0.5xMass with research and funding.