You're not missing something. The MDE app is NOT disabled-friendly, even if you are defining "disabled" as simply farsighted. For starters, it has no Settings option; the only thing you can set is language preference and whether or not to get notifications; you can't set the notifications to be anything other than sounds (normally I have my phone set to flash for notifications, but that doesn't work with MDE.)
It is not possible on every screen to enlarge text within the app, not by permanent setting, and not using finger-spread page zooming (it works on some screens, but not all: you can enlarge the theme-park reservation screen, but not the Mobile Ordering one, which is bass-ackwards, since you are much more likely to be using a phone to order food). It also has a tendency to hang when used with the phone set to high-contrast mode.
St1tch, the OP related an incident about a lost charging cord, which of course is on her, but it all fits with the reality that if you cannot comfortably rely on being able to consult/use a smartphone to make all your in-park decisions, then your ability to enjoy the parks to their fullest is diminished, and the galling part is that that is not accidental, but designed-in to the present day park experience. If you are going to sell power-related phone accessories in the parks at all, then you need to sell them for all types of phones, not just one brand. (I'm not going to extend this wish to things like cases, just items that allow phones to actually function.) And if you are going to create an app that uses this much power, then the power banks sold in the parks need to be up to the challenge of providing it. A 2600 mAh Fuel Rod isn't going to do that for a current-generation smartphone.
It's not just about text size, it's about forcing a guest to both carry and frequently use a fragile, expensive device that requires an independent power source. If you are going to make it so you cannot take advantage of the majority of park activities without it, then it should at least be designed so that it is less likely to fail. Step 1 for that would be stripping down the excess content & visuals so that power & bandwidth consumption is reduced, and beyond that, creating a settings menu that allows disabled guests to decide for themselves how they can best interact with it. The Disney Company prides itself on accomodating the disabled, but this is one area where they have really fallen short.