"The Google user has a problem and is actively seeking a solution; the Facebook user fits what you believe is the demographic profile of someone that might be interested in your product."
That's all well and good, but at the end of the day I can Google "Maserati Dealer" and yet have nowhere near the income levels required to purchase one.
"Traffic from Facebook ads is notoriously difficult to turn into cash precisely because of this. Most of their advertisers measure ROI in terms of shares and likes, not new users or product sales."
As someone that works in the industry this patently false. We measure Return on Investment in dollars not vanity metrics. ROAS is going to be your most common topline stat which is used (stand for return on ad spend with return meaning revenue).
"Advertising products/services on Facebook is a fool's errand for almost everyone, except for those with an extremely broad target audience."
Again very very wrong. In fact the most successful campaign I've ever run (3 million+ in revenue that was 300% ROI positive) was a relatively small niche market that was less than 200,000 people.
Now if you want the real reason Facebook seems to not work. It's a few things.
1. The people that raise their hand up to talk about Facebook ads do so because they're frustrated so all the things you read tend to be very polarized and negative.
2. Mostly amateurs are buying Facebook ads. Professionals routinely do much much better even in B2B niches.
3. Just because you're product didn't sell doesn't mean that the platform doesn't work. It routinely works for thousands of advertisers of all sizes every single day. I would encourage you to ask if it's the ad platform? Perhaps your ads? Perhaps your targeting? Perhaps your product just hasn't found product market fit yet.