Yeah like Amazon being such a failure because they have to pay for advertising.
You seem to have confused buying backlinks with advertising. The two are not entirely equivalent.
Advertising is not the same thin as purchasing backlinks at all, yes the waters do get muddied a little when it comes PPC, as PPC is associated with advertising, but the difference being you're actually paying for when someone clicks on a link to your site , hence you can measure the effectiveness of you campaign and you can also continue to several variations and work to optimise the conversion rate.
Interesting that you chose Amazon as an example, especially when even Jeff Bezo's himself attributes Amazon's rise in popularity to their Affiliate Program in the early days.
A program in which Amazon did and still does pay for people to put links on their site, and pay commission if someone clicks on a link and buys products from Amazon.
This effectively enabled amazon to get literally get millions of links and build authority and for others tot participate in the success.
Yes amazon, pay for advertising now, but in the early days of starting out, it didn't. In fact, the whole reason why it was called Amazon, is because that was a name that would ensure it was listed in the opening pages of phonebook back in the day, without Bezos having to pay for the advertising!
By paying for advertising now, enables amazon to effectively communicate with it's customer base, which yes is a difficult challenge especially now, when the customer base spans the entire globe and are on 1000's of different channels and devices.
So coming back to buying links, it's not really the same thing. PPC of course does work, but analysis conducted as recently as this year, indicates that effectiveness is gradually in decline, as more people are making use of adblockers etc, to effectively to avoid the annoying ads.
I admit, there is no one piece of advice in this area which is 100% correct. But I can assure you that paying for backlinks actually has zero benefit.
It doesn't mean to say that, engaging in proactively buidling quality to links to your website is not a worthwhile practice. It's just not the same as paying for backlinks.