I am doing BE for a year now, I can play most of the exercises pretty well, but I do not improve a lot. What use is BE then?

I often see that people think they do the exercises right but actually go on much too fast. More often than not they are not following the instructions carefully enough. The best thing you can do in such case is to check every part of BE very carefully with what the book says. Even if this means that you start all over again. Is your Lip Clamp correct and do you do it every day? Is your LCS correct: listen to the sound, a squeak not a buzz. Are you doing RI correctly?
A lot of people fall into old habits again to make a tone happening in RI.There is no room for fumbling, there. It is either good or useless.Put your mouthpiece on the LCS setup (both with squeak or hiss is OK) and try to produce a tone this way. Is your RO sounding weak? RO is not a loose embouchure, it is an extreme forward and focused way of producing a tone. Is your TOL squarely against your top lip? Is is possible that you have no idea what and where and what you touch with your tongue? (This is a not uncommon phenomenon. To check this, start with putting your tongue against your top lip-check it in a mirror-place your mpc, blow and release the air by moving the tongue downward or slightly backward. This is where you should place your tongue in TOL). Check your sound with the sound on the CD and read the text carefully again.

Failure can be caused by using other embouchure methods . Things like free buzzing or mouthpiece buzzing and Gordon/Stamp-like methods, can be counterproductive. When you start with BE it is better to use only BE as chop development and play normal studies, concert pieces and play-alongs to integrate the new chops in your regular playing.
Of course there is a possibility that your playing level is very high already (you are already playing 'balanced' without knowing it). In that case the effectibveness is probably nihil.
If you are able to do all the exercises exactly as described in the book, then it is hard to believe that this doe not have any effect on your normal playing, but of course, I have not seen it all.