Galatic stagnation
From my memory of reading the books and the comics, the Empire had been controlling technology via kidknapping any Engineers/scientists that could improve their military potential. Additionally as the Emperor was a xenophobe with a pogrom of crushing any non-human advancement and limiting non-empire ship production then it isnt really suprising that the tech has not advanced
Given that this film is set after the collapse of the empire then you would expect for what quality Engineers remained alive once total Empire control was broken to return to their homeworlds. This scattering of expertise would, I would suggest, stall tech evolution and the availiblity of quality expertise for at least 2 generations resulting in a period of replication of existing trusted tech before the new generations can produce something that is so obviously better that it will be trusted over the known tech.
As to the crappy lightsabre then I would presume that since the sith grow artifical crystals and the production of these would have died with the Empire this weapon is a relic left over from long before the republic fell.
Personally I don't like the idea of a Disney starwars and Bad Robot productions give me motion sickness but to be fair I dont think anyone can knock them for not changing the whole SW universe on their first attempt, tech stagnation I would suggest would be following the lore.
Biting the hand that feeds IT
