I use either, depending on the situation. Brush on polyprop that needs pile lift as well, bonnet on wool/nylon. Brush to deal with pet hair, embedded fluff and sock fibres
Nothing wrong with rotary cleaning on most carpets after they've had a few years' wear, as long as you spray it up nice and damp to lubricate.
Obviously with wool, the newer the carpet the more risk of noticeable texture distortion. In most cases if you need something as robust as a rotary to agitate a wool carpet, the chances are it's not been treated very well and it really doesn't matter if you slightly distort the pile as long as you get a good visual clean.... the customer wants the carpet looking cleaner! You've just restored a carpet for a fraction of the cost of buying a new one, so if you've accelerated the signs of wear a little bit that's an acceptable trade-off. I think most would agree with that, rather than sticking to "safe" methods and shrugging shoulders when it doesn't come up as great as it could have.
Same mode of thought applies to higher pH cleaning products, you gotta do what you gotta do! Just make sure you know what it is that you're doing, when you gotta do it, that's my philosophy
