I realize the damage drop is significant.
Would having a dedicated turret damage research for each laser turret be enough or does it need a damage bump?
No need in my opinon. If compare actual damage, advanced laser takes almost 10 times more power, but gives 10times more damage. Attack rate is 5.5 times lower, but it has AOE.
Also would have a mid tier laser beam turret in addition to the standard laser turret be helpful?
Also you had mentioned in the other thread about bullets failing at higher levels, do you have recommendations on how to modify them?
I think, that everything is fine. The problem is your mod users setting max biters end level and variations :-)
Level 10 biters require space science upgrades for all turrets and damages and probably some factorio-specific competition (but instead of green/red/blue circuits per minute user should run for production of bullets, shells, rockets and delivering them to frontier in time).