I agree what Low-Tech feels underwhelming, but my major opinion is what nerfing Mid/High-Tech is big no, I mean actual ship stats, problem are not with them.
Low-Tech ships have too many drawbacks, bad flux stats, its barely can support its own weapons, low shied arcs, low mobility and they are very vulnerable in the back and being surrounded, and AI can't properly use its strength and Burn Drive which misuse can put ship in bad situation. Also main offender is skills, most of skills are gives benefits mostly for Mid/High-Tech, new zero-flux boost bonus in Helmsmanship which AI can't properly utilize, which means what slow ship will be always kited, nerf of armor skill in RC15, way too many drawbacks.
Also about different subsystems, rather than burn drive, I liked how they made in Archean Order, instead of burn drive each ship have own subsystem, XIV Legion have damper field, Dominator and Onslaught combat capacitor which increases firerate, flux stats and speed, and XIV skills actually differs from not XIV versions, for example XIV Onslaught had laser beams instead of ballistic cannons on its arms. Also I liked from that mod idea of reloadable missiles too, I personally avoid them in vanilla game, because they are limited, and for myself seems more logical add some hullmod or vents/capacitors rather than have limited weapon which AI probable will waste anyway, only exception is Doom, where I can put Reapers for insta-kill variant.