remember that the jedi where there a 1,000 years and already have light saber, so they're tech is a lot more advance.
"For a 1000 generations the Jedi were the guardians of the old Republic" not years.
Irrelevant anyway. Time does not always lead to technological advances. Some societies progress technologically slowly, consider the Roman and Chinese empires. New inventions and knowledge can be suppressed as "dangerous" to the established regime.
The light saber as a "laser sword" makes no technological sense. What causes the beam to not extend until it hits something? Why does the blade grow from 0 to full length in a time that a human can see the growth? How come the "laser" blades
physically collide instead of pass through one another? So the light sabre must be something other than the laser sword it is portrayed as being.
In addition you must remember that the Federation has access to much more advanced technology that they
choose not to use. As one major source consider Norman and the other androids from ST:TOS I Mudd. They are under Federation control and programming. They have technologies such as "warp engines the size of a walnut", androids that the Enterprise sensors cannot tell from living human flesh. The ability to put a human brain in an android body and sustain it for centuries.
There are two possible reasons why the ST Empire has larger ships, the reasons could of course be combined:
1/ More planets which allows some to be dedicated to single industries. An entire planet that only builds starship hulls would be able to build much larger ships than one that builds starships only for it own needs.
2/ Droids as slave labour. Build them to the intelligence level required and no more. Droid slaves building arbitrarily large numbers of other droids on uninhabitable planets with no consideration of environmental damage could build huge numbers of droid slaves. Take those droids into nearby space and dismantle moons and asteroids for raw materials and you can build structure of sizes as vast as your technology will allow to hold together.
Of course just because ships are large does not mean they are well designed or well built.