You need 50m, 150m, 200m, and 300m repeats too.
For most, speed will be the limiting factor for getting under 2:00 and 1:55. You need to be able to cover 200/400m in 25.5/54 to break 2:00 and you need about 24.0/52.5 to run 1:55. Once you have speed like this, the longer repeats and tempo runs you are doing helps you to stretch out that speed to a 2-4 lap race distance, but you aren’t gonna run sub 1:55 even if you are the best marathoner in the world if you can’t run faster than 56-57 in a 400m.
You need to get to a place where you can run 200m repeats in 28-29 and not feel like you are sprinting.