Other options can be just as expensive, yes, though many are cheaper. My main point is that the perceived value of a product goes beyond questions of price; it's also (and I would say more so) a matter of what one is actually looking for. An all-inclusive holiday in the Dominican Republic is an alternative to Disney, not a substitute for it. If someone is equally open to both options, then of course they'd do well to choose the cheaper, but that kind of approach makes little sense if it's specifically WDW you want.
Well, sorta. Both are vacations. FYI, I've been going to WDW almost since it opened and WDW was just MK, so Orlando was only 2-nights of a longer visit to FL. Even in the dark ages of the 1970's, WDW was just one tourist option among many somewhat similar options.
While DR is a bit of a different experience, I've always lumped WDW in with all sorts of FL options. In the 1970's it was Sea World, St.Augustine (Ripley's, the fort), Vizcaya, Miami Serpentarium, Gatorland, Lion country Safari, Everglades NP, and many others. The FL beaches were also a part of every visit.
Over the past decade, I've paired with WDW with Universal, Sea World, FL's state and National Parks, many FL beaches, water parks, etc.
I'm not quite sure how to say in a forum, but budget and variation are always important factors when I vacation. I often choose to stay offsite in Orlando, partly for budgeting, but always because I value variation. IMO, a beach view hotel room beats any room view WDW has to offer.
All of this is to say, for me personally - to use your wording- FL offers many great substitutions for WDW, especially because they often cost much less and offer greater variety.