There is some limited truth in this - by choice, for example, I would fly a carrier offering an A380-only service long haul. But the routes with this choice are limited (and now declining!)
In almost all other contexts you'd have to ask how easy is it for a customer booking advance to know what equipment will be used on a route on a given day? The most obvious variable presented at time of purchase is price, differences can be substantial and not correlated in any transparent way to seating except in re economy v. business classes. Pax are not given the ability to make the choice you suggest.
As for 'value' - well that term refers to a subjective judgement for which the divisor IS price.