Following this new Customer Demand series with great interest.
Demand is the part of the business triad I am most familiar with, so Sales Safari seems quite basic to me from watching the video, but as you point out, it does look like a great resource for those very new to marketing and customer understanding more generally.
A few thoughts…
The article ends with this quote:
“The job of sales and marketing is to seek out and then filter customers who are the best fit for your product.”
I would argue that marketing is not just about finding the customers who are the best fit for your product, it’s also about defining the product to be the best fit for customers. It’s an iterative process. This is what you seem to be outlining in the essay and the approach to customer demand as a whole.
It reminds me of an old saying about two ways to approach marketing (prob by P&G/Unilever):
Are you making what you can sell, or just selling what you can make?
Sales Safari seems very much in the spirit of the former - ‘let’s make what we can sell’ and so feels like ‘proper marketing’ utilising the 4Ps of product, place, price, and promotion, rather than simply demand generation / ‘selling what you can make’ which is usually just about promotion.
Detachment — as you say this is harder if it’s your product. I’ve only worked inside an org on product strategy and product marketing once, and the rest of my career has been as a consultant, so detachment comes a lot easier! Perhaps I should think about my role as ‘detachment as a service’. 
However, I also wonder if detachment is harder in software / technology businesses, compared to say CPG businesses, which historically have been the masters at understanding, identifying and capturing customer demand. Competitor CPG products within a category are often functionally almost identical, often being produced in the same factories as the supermarkets own brand versions. So it’s harder to hoodwink yourself that there is real functional differentiation, hence detachment comes easier, and more attention and investment on intangible differentiation via brand, packaging and comms.
Research IS exhausting! — I was vigorously nodding in agreement when you talked about how exhausting running this type of customer research is. I have had to politely explain to clients and colleagues many times that NO, 6 or 7 hours of customer interviews in a single day is not feasible!
BigQuery example - I think a proper experienced researcher would also pick up on ‘unpredictability of costs’ being a pain point in this example. But I think your ability to zero in on the fact it’s THE pain point, and not just a possible one alongside high prices is also about a wider commercial acumen and understanding of the business model, cost structure and the industry. This is where an insider doing the interviews has an in-built advantage, but it’s also about context beyond just research technique. I.e. You can teach the habit of looking for things unsaid, but without the commercial insight you were able to draw on, they still might not reach the same conclusion you got to.
@overandout I agree with Cedric’s recommendation to interview existing customers, although depending on how new your business is, you might not have very many. If this is the case you could also interview customers of your competitors — I have found this particularly useful in the past. Ideally you’d want to interview the specific competitor customers you want to steal for your business, but even those that are slightly different (e.g. a different worldview / segment) will still teach you valuable things about the market. And may help you refine who you interview next.
I would also say that there are categories of products that are simply low(er) interest. CPG products typically fall into this category ime, although there will be exceptions (e.g. dealing with a specialist use case like a skin condition). Historically many CPG purchase decisions were made in the final few minutes/meters of the store, which is why the bigger brands pay so much for premium shelf space at eye level, and spend so much on advertising and promotions to be recognisable. In low interest categories people will ‘satisfice’ rather than maximise - and recognisable brands are a great shortcut to doing this.
Without knowing specifically what your CPG products is, I would assume you are less likely to find watering holes, compared to say the B2B products such as those Amy discusses in her video and will have to rely on customer research primarily, unless you are targeting a high interest pain point or niche use case.