Can we all agree with the premise that a DM having less rules constraints on adjudication means there is greater flexibility in a game?
*Note there are pros and cons to greater flexibility
Eh. I genuinely don't know about that. "Flexibility" is a difficult thing to define. Not trying to be pendantic, I genuinely mean that "flexibility" can mean very different things to different people.
For example, I've had multiple PF/3.X DMs who completely burned out on running that system. They felt that,
because the rules were so open-ended and had so few limits, they were screwed. If they just went all out and created whatever they wanted, it would essentially guarantee they'd crush the PCs no problem. If they tried to make something balanced and effective, players would easily roflstomp it with a ridiculous combo of spells, items, feats, features, etc. They had a great deal of "flexibility," and yet they felt 90% or more of the roads they could take went somewhere frustrating or disappointing.
By comparison, in both 4e and 13A, I've seen DMs genuinely feel inspired and excited, because they realized that there was very little they could do that
wouldn't work out. Sure, things are somewhat more constrained than they are in 3e (or 1e or whatever edition one wishes to compare), but many of the avenues cut off were the ones going to unfortunate places. Instead, they could move forward with confidence, doing
whatever made sense to them, because the system had their back and would provide a very high likelihood of doing something
cool in actual practice, not just in theory.
So...is the former "flexible" but requiring "caution" and the latter "inflexible"? Or is the latter "flexible" within reason, and the former so open it verges on vacant, to reference that old saying about keeping an open mind?
And "flexibility" isn't the only thing that can cash out like this. For some, "complexity" is absolute anathema--it means busywork, "filling out your taxes" in order to play, comprehensive and utterly needless overhead for absolutely no gain. For others, it's a delight, the richness of a system with many parts that need careful consideration and which rewards skillful manipulation thereof. For some, "simplicity" is a godsend, a respite from the tedium and a chance to finally cut loose and play the way
they want to play, regardless of what some pencil-pushing designer thinks. For others, it's a nightmare, a prison of inability and monotony without recourse that drains away whatever interest the game might offer.
This makes it very hard to unequivocally support any attribution of virtue, even if
in principle the idea of something like "flexibility" or "elegance" or "ease of use" should be universally desirable.