Well I'm just not interested in the idea of placing limits on where stories "should" go based on the limits of past and current writers.

The hope is always that stewardship of the universe will one day fall into competent hands, and you can never know when that day will come. The future isn't written yet.

For all we know, MK10 may have a different team of writers than MK9 did. They may see MK9's story mode as a "success" enough to be even more ambitious, do longer scenes, attempt more depth, switch character POV more often instead of that chapter shit, you just never know.

If they can make it work then that's fine. But thus far I, at least, feel they haven't proven to be able to and so, if they are to continue on this path, should not attempt to until they can.

Well how are they going to know when they can if they stop trying? Writing isn't a science. Good writers can put out something that sucks after a long career of writing good things, and bad writers can get better, or get lucky once in a while, but like all art, constant practice is required.

By writing it then leaving it out of the final product if it doesn't work in the overall scheme of things.

That's not really viable if the relationship actually matters to the plot.

For instance, rescuing Kitana is Liu's main motive for fighting Shinnok in MK4, and for sticking around as a ghost instead of going to the afterlife in Deception. And in MK9, it's her death that is his motive for deciding he's had enough of Raiden's ineptitude.
And a good story is not made of modules you can just insert or remove at will. Everything should matter. Deleted scenes are one thing, but there should never be such a thing as a whole deleted subplot.

The thing is, however, that If the relationship is matters to the plot then they have already managed to take a step in the right direction compared to where they are now.

Smoke and Rain
Kitana and Jade
Mileena and Skarlet
Sub Zero and Scorpion
Chameleon and Reptile