for context - i have a hardware product in a niche industry and have noticed that over the past 20 years it has become really hard to get any visibility at all online unless you buy ads and/or pay so called influencers to do videos (i.e. the situation is now pay-to-play). i wonder how other founders are experiencing this and what they have done to deal with the situation.
From experience I've seen clients who've hired a SEO agency years back, and have never stopped paying them due to the fear their traffic will bottom out. I do believe SEO agencies offer value, however base level offerings such as technical suggestions and keyword strategy don't get businesses far. Typically the people who pay for the base level offerings don't have the in house talent to write solid blog posts / action the suggestions. Plus most base level offerings could be augmented by paying for a tool like SEMRush yourself, and letting the automated reports run.
Long tail searches with little competition are the easy wins. Popular keywords will take time and effort, but usually with alot of work involved.
So, the trick is to be patient and do quality work. It will show.
Generally if you're thinking that way you're going to find promoting your web site difficult and expensive no matter what. In the case of paid advertising, for instance, that other guy who wants to rank #1 is going to spend as much as you if he's as stubborn as you and between the two of you you can drive the cost of advertising into the stratosphere.
Where you can win in SEO is developing a site that ranks for many phrases (thousands!) Consider a blog, for instance, where you might have a few hundred articles and each one is like a lottery ticket. There are thousands and thousands of queries that might bring people to a blog article so it adds up to a lot of traffic, if not laser-focused on the purchase imminent user that you want.
As for white hat SEO, I think it still might work as long you have a nice budget for it or happen to be really good at it. You have to beat a lot of Goggle ads and a lot of black hats, not just competing content.
You can spend a fortune on developing an SEO strategy and trying to game your way to the top of specific results. But if you are patient, build your website with some basic good practices, and write regularly on topics people care about - you can still build pretty okay traffic.
Should you rely on just SEO? hell no.
Hire an SEO early and do NOT outsource this to an agency. They will bleed your budget and deliver very little.