The advertisers would disagree..
Sure the advertisers disagree, or they'd fire themselves.
A few brands in the past thought this and stopped advertising. "People" forget quickly - and even more quickly when a competitor keeps advertising.
Not necessarily. For example in the UK (and maybe the World) Stihl is the best brand of outdooor machinery. But I have never seen an advert for Stihl in the media. Yet they dominate the professional market because of their reputation which people do not "forget".
1 - People are born and people die.
Adverts are not the only way that people learn of a brand. They learn from other users, reviews on the web (amateur and profesional) and simply Googling for makers' web sites. If I want to buy a camera I would Google for "cameras" and find the web sites for Nikon, Canon etc. I don't think anyone is complaining about advertising in the form of makers' websites describing their range of stuff.
2 - People who do use XYZ product are likely to use more or choose a specific brand if they are constantly exposed to it. Think "Bud/Coors/XYZ light please" at the bar. You are more likely to choose something that is "top of mind" and advertising keeps it top of mind.
Nope. Talking beer, what is top of my mind is the beer I like. I've tried many beers and II prefer London Pride - but never seen it advertised.