Being able to play crummy old arcade games on a computer is more than I could ever imagine?

Wow.
Ever hear of the concept of "context"? The MAMEDevs have given more to the resurrection and preservation of the these old games than X, and apparently yourself, could ever imagine. If you haven't done it yourself, you have no frame of reference for the sweat and tears (hopefully no blood) that it took to get this project where it is.
Also, if you think the old games are "crummy", you are obviously trolling the wrong forums. Some people think knocking a steel ball around on a gaily decorated board full of switches and lights is a pointless endeavor as well (not me, I wouldn't trade my fully restored "High Speed" for anything.) So the whole "glass houses" thing should probably be considered when you make statements like that one.
The Analogy is pretty much like the Hotdog Stew.
I'm taking you to mean that it is ridiculous and no-one should make it?
The gameplay " IS " Destroyed when you do not use the intended controller. And as for destruction of history, that is left for time. In time, when someone fires up mame to see how 720, Sinistar..etc.. worked... they will not only be given the wrong control information... but they will experience the game in a way that was never intended.
The analogy is more symbolic to the individuals experience 'now'. We all cant experience sitting in and driving a vintage Classic Car. However, if its possible to recreate that experience... then great. But to alter that experience by stripping out a manual shifter to an automatic... is not true preservation or correct representation. Responsibly speaking, its a very bad thing to do, to alter History based on Personal opinion.
No, Steve, nothing is destroyed. It's all still there, just the way you remember it. Nobody has incinerated those machines, or their controls (well, they might have, but it wasn't the people you keep screaming at.) No king of any land has formally decreed that the only 720 that shall ever be played or remembered shall be the one in MAME. The controls for 720 are documented in many places on the web, and on the still existing original machines as well. The way the control interacts with the original code is also still present. There is simply no way for Joe 12-pack (times are rough) to get to them. He needs to step away from the instant gratification box and learn to do a little coding. That is not the same as destroying anything, unless you are counting your own personal "treasured memories" when you boot MAME with your original 720 controller in your hand, expecting it to simply work because you are you.
There is no PC analog for this control, in its original form. It's not a mouse, but a superset of a mouse. It's a mouse+, with the + being something that cannot be achieved with common PC analogs. So the current control scheme, via the translation layer, is assigned to the common PC controls that will actually allow one to test/play the game, without the magic original control. You are clamoring for an option to essentially hack in support for something that you, and very few others, own, or likely ever will, at the expense of convoluting the code and making it less manageable. I personally think they should map the index pulse to a digital input and call it a day, and have suggested it in the past. But they consider that a "hack", so I accept their view. It is their project, after all, not yours. Your realistic options are to maintain your own build, which they graciously allow you to do, or buy an original machine. You shouldn't be surprised when anything other than that is called out for what it is. At this point, I wouldn't be surprised if your relentless hammering on them has kept something like what I suggested from being added, just to keep you miserable.
Personal Opinion often does not equate to "Preservation".
It also does not often equate to "fact". One can argue that the cabinet dimensions, wiring schematics, artwork and myriad other properties of the cabinet are equally as important. But I don't see you expecting the MAME Team to "preserve" those aspects, as well you shouldn't because those are also not included in the project goals.