I don't have an "opinion" on maximum tea amounts, I found several sources that all recommend the same usage rates, and the recommendation not to exceed. Too much tea will put the SCOBY out of balance, so this advice makes sense to me.
I didn't think it was strange that I mentioned the books ratios, because they do very clearly say "use this much." I don't find that strange. Obsidian had commented that she had difficulty finding recipes that say how much to add, and BBoK says how much to use. I haven't had problems with flavoring following their recipes, but taste is subjective. I also have a sensitive nose, so I may be able to taste their flavors better while others with less sense of smell may not.
It's been several years since I read the book, and as I have found with other books by people who also sell ingredients and supplies, their advice is geared toward you buying their wares and buying them often. This was how I read their book compared to a significant amount of time spent reading other sources. Sorry I can't give specifics (the book said this, but these sources said that), as I said it's been a few years, but I do remember some conflicting advice, and further research showed me that there are easier/better ways to do things. It probably also helps that I live with a beer brewer, and am part of our local beer brewing club [while there are differences between beer and booch, many of the principles are the same, and many shared their experiences and knowledge of booch]. I'm not an expert by any means, but I have read alot, done alot, and had to correct alot of my own brewing mistakes. Some of those mistakes happened following the BBoK. This of course, is my own personal experience, and while BBoK is a good starting point, I would not make it my only reference. I've found this true for many things - sourdough (which I've just started my journey on), soapmaking, and raising children
There is no one definitive guide, but with a bit of research and sometimes trusting your own intuition, you'll end up with results that are pleasing and can be repeated successfully. (Although raising children still has me a bit stumped. Hopefully by the time the grandchildren arrive I'll have it figured out.)