[heliodor]

The main point people make about differentiating your digital product is to not compete on price. A lower price means less money for advertising and marketing, so a losing proposition.

What you're proposing with the one-time upfront fee model is to compete on price, so smart entrepreneurs steer clear of that model.

[exclusiv]

I like SaaS but one time has the advantage of being able to use more money on growth. So if you have your acquisition dialed in it can be advantageous to offer a larger annual or lifetime model.

[Denzel]

Have to disagree with your conclusion, counterpoint being Jeff Bezos who maintains a number (a majority?) of business lines that compete on price.