I can see nothing wrong with the book, it's a great piece of work, and if you have the kind of personality to sit and work with it religiously, I'm sure great results are possible. However, if it's not for you, there certainly are other ways to become a good or great player. I wonder if we asked the past 10 years of top players who have won the GFA what methods they used how many would say they used Kitharologus. I'm guessing very little, which tells you there are many other ways to greatness. I've been to master classes where the teachers said they didn't practice exercises. Odair Assad said he always felt like he was wasting time practicing scales and exercises, but then said that of course he practiced the scales that were in the music.
In my experience many people don't know how to take the piece they are working on and turn it into 100s of exercises. All the exercises you need to play that piece are in the music you're playing if you find them. Make sure all your fingerings are notated. Then, make an exercise out of repeating small sections that contain a transition. Sometimes this is just 1 measure plus a beat. Then two measures. Then the next measure and a beat. continue. Work on each chunk until you can play it 8 times without a mistake, then move on to the next chunk. String smaller sections into phrases, but always focus on repeating things that have transitions because that's where the difficulty lies -- chord changes, shifts, string changes, etc. Be sure to memorize the chunks so you can observe each hand separately and fix problems you see. If you practice many differing etudes and pieces, this kind of practicing effectively presents you with all the different techniques required to play music on the guitar. And you're not wasting time on techniques that are outside your repertoire. I'm not ant-method books or exercises, I do some of that too, but I prefer this approach to get the result I'm looking for, which is playing music.
An eyewitness will often only see what he already believes to be true.