It is only a complication if you don't train.
If you have trained for only one option then your chances of choosing the right option is pretty high because you just do the only thing you've trained to do.
If you train for two options then, in a stressful situation you have to choose the proper option from amongst the things you've trained to do.
It's not a matter of how anyone sees it, it's simply that picking the right option when there is only one option to choose from is simpler than choosing the right option when there are multiple options to choose from.
One person new to carrying. Carries one style
One person owns two styles and changes but trains regularly on both platforms.
Who has the greater potential to screw up?
This is defocusing the discussion. The question isn't whether or not training is better than no training. Generally speaking training is better than no training, as long as the training is good training. But that's really not the point.
The question is whether carrying different kinds of guns is better than carrying one kind of gun.
I understand the argument of the more variables, the more potential for things to go awry.
And that's the answer to the question.
But if someone fumbles in a high stress situation, carrying his/her second platform, do we know that was the cause or was it the situation itself?
It doesn't matter what the cause was because we're not doing a post mortem, we're trying to figure out a course of action that will help us avoid the fumble in the first place.
The point is that
needlessly introducing additional variables
needlessly increases the potential for things to go awry.
I don't think the answer is so clear cut and packaged so neatly into "must be the second platform" argument.
I agree. It could have been anything that caused the fumble. But the fact that there's already quite a lot of potential to screw something up is a very poor rationale for adding MORE potential to screw up/fumble.
Is it WISE to carry guns with different manuals of arms? I don't believe it is. Will it automatically cause a problem? No, of course not. But it DOES increase the potential for a negative outcome and in a self-defense scenario there's already plenty of negative outcome potential without voluntarily adding more.