Hazelnut pie, the dentist on this thread is probably more relaxed about very limited use of bottles precisely because of his/her experiences seeing actual patients.
Public health advice is based on the lowest common denominator. The people who work in public health see some bad issues caused by overuse of bottles (toddlers dragging grubby bottles around all day and sipping on them all night, tooth decay caused by drinking from bottles at nighttime, toddlers not getting onto proper meals because parents find it easier to keep handing out bottles and pouches to keep the kid quiet in the pram/car seat, toddlers over-consuming cow's milk in bottles and getting anemic...just C&Ping the above!). They also know that the kind of parents who allow their children to get into the above habits, tend to be people without high levels of education who struggle with things like reading comprehension, and who are likely to have difficulty reading/understanding/remembering complex nuanced messages like "It is OK to use a bottle a little bit, providing that.... blah blah blah." So the safest and simplest thing is to just boil the advice down into a super-simple easy-to-remember slogan like "no bottles after 12 months."
Same with everything else. Baby walkers are fine if you use them a little bit and supervise carefully, but complicated statements advising people how to do this, may not be read or understood properly by precisely those parents who are the most likely to do daft things like leave a baby stuck in a walker for half an hour while they go and cook dinner in another room. So it's safest to just say NO BABYWALKERS. Yet many people do use them in a very limited way without problems.
Cups-only from six months should be fine for a BF baby who is getting most nourishment from the breast (my baby had an open cup only--from five months! She wouldn't drink from a bottle), but if a fully FF baby was on cups-only from six months, I would be a little bit "huh?" Babies generally do not drink as much from cups as they do from bottles (that is indeed part of the reason why it is recommended to bin or strictly limit them after 12mo), so if a 6mo FF baby were on cups-only, I would be concerned that they might end up not taking enough milk. Bottles are also a source of psychological reassurance to very young babies, just like the breast is.
I seem to remember that Gina Ford book nagging on about how parents should give only cups to babies right from very soon after they started solids at 6mo, and my feeling was that she was perhaps basing her recommendations on old-fashioned weaning schedules that held sway many decades ago (where the baby by 6mo was mostly on "jars" with hardly any milk--and probably cow's milk, at that).
There is room for a sensible middle ground here.