I don't know V. Gunaratana's book really well, so I won't go into that. You'll have to ask him what he means. But for now I would point to his analogy of the muddy cup on the next page. What do you do to settle the mud? You put down the cup. This means you back up, you let go, you don't disturb the water; very similar to the bathtub I gave before (I'm quite sure the still water analogy comes from suttas originally). And so, you don't get 'doing' involved.
So that aside, I can respond in more detail to what I said. I'm not saying focussing is wrong, I'm saying willfully focussing is not useful, because doing things with willpower is not creating peace. You can apply the mind to the breath, it doesn't always have to go automatically. However, in the end the mind will have to stick by itself to really get settled, whether you applied it or it went by itself. If it doesn't like to stay there by itself, it won't. You can force it back for 100 years, but it just won't stay if you treat the mind like that. Perhaps it will stay for a few minutes or even longer, but it won't enjoy it and I don't see meditation progressing then. It'll be more like a struggle, which meditation isn't really supposed to be as far as I'm concerned. It's about being kind to yourself and about being happy.
So instead of trying to go against this idea, why not try it? As I understand the method you applied so far didn't really help, so at least you could give an alternative a go. By focussing on the present moment, see if the mind will go to the breath automatically. I can see how it may sound unconvincing, but it really does happen and not just to me, so I hope you can experience it in some way or the other. Otherwise there is still plenty of peace before going onto the breath.
Do please note that the difference 'you' and 'the mind' in all the above is really artificial, which could give rise to some confusion between different explanations of different people. In reality there is no such a 'you', so if a teacher says 'you' do something in meditation, that's actually the mind doing it. But initially I think it can be useful to make a distinction, especially if you get a lot of stress out of meditation, that means you are trying too hard.