The 250+150 workouts are pure 400 metre work. Your results this year show a significant improvement in your 400, and no improvement in the 100. That should be a clear answer of what 250+150 workouts do- help the 400 and little else. Don’t get me wrong- they can be useful to the 100 and 200 in a non-specific sense for overall fitness and conditioning work. You get fit off those runs in a hurry! They will not improve your 100m or 200m time directly though, (unless you are in Mark Lewis-Francis shape and need to drop 30 pounds). This shouldn’t be hard to argue- as your 100/200 is the same as last year.
Charlie mentions repeatedly, “Speed is specific to itself.” You are not hitting anywhere near the same velocity in a 250 metre run that you will hit in the 100, thus it’s difficult to improve your 100 speed if you’re not actually running in that speed band (10m/sec+) very often. Check out “Key Concepts Elite Edition”, there is a ton of talk about this.
If you want to develop speed, you are going to have to spend time doing full recovery alactic speed work under 8 seconds in duration (60m-70m for you), and some full recovery speed endurance work as well. It sounds like you aren’t hitting those distances often enough, and with enough overall rest or freshness to make improvements. If the 100 and 200 are your races and you want to run faster and your coach won’t change the program, perhaps try to get a few extra races in, which will allow you to skip some lactate workouts hopefully.
I can tell you that during the winter when I started doing the KitKat 400m program detailed in the Lactate Threshold thread, there were lots of split runs similar to your 250+150 work, and no true speed work until after the first 12 week GPP. My 60m speed stayed exactly the same, but my 300 dropped almost two seconds in the first 12 weeks. Thus, you need to do alactic speed or you aren’t going to improve it.
Thus, if I want to improve my 60 next year, I would need to add in an acceleration / speed day once a week from the beginning, which I will certainly do next year.