Mechanical removal is a lot of work, but it does remove the nutrients from the system. If you have the flushes you talk about, and aeration, you should be removing some of the nutrients that way, but it looks like there is a lot of nutrients remaining even after a few years of aeration. I would start with some mechanical removal and see if you can make a noticeable difference.
Oh, I would look for a different pond maintenance expert. There are several here on PB that are in your area. They will be able to work with you to attain your goals in a reasonable amount of time.
