Maybe that will be true over a looong period of time, but without getting too deep, I imagine that all companies and IPs with marketable products will generally always have a niche consumer base purchasing from them.
Stuff like Pokémon has endless lines of figures, cards, and plushies aimed at all age ranges that they will always make bank from. Of course that has a lot to do with their parent company’s sheer mass and breadth of multimedia content, but I think as long as a company continues to invent, they’ll gain (and grow) a profitable consumer base.
With that being said (and I’m definitely not trying to argue against your point), I’m not entirely sure how differences such as size or scale within an established product line would necessary need to change to cater towards generational preferences or even have much direct impact on profit margins for a given format.
I’m still pretty new to this industry and am only in my early 20s, so maybe there’s some things I clearly don’t have any experience from. But my real point is, I feel like the entire collectible figure scene is becoming more accessible (albeit more expensive) and will probably maximise monetary benefits by catering to as many scales as possible (thus keeping 1/6 as a forerunner), allowing them to focus on maximising the potential consumer base versus catering to any specific crowd: new, old, young, or… well, old again