Flash does scale with gear. There is some fairly compelling evidence that it scales with weapon damage (and FoF, which is +dam) as well, so it's a bit fallacious to claim that it doesn't scale or benefit from any number of CDs. The only one that makes a reasonable case for not working with Flash is Internal Release because we're pretty sure that Flash can't crit (meaning that it generates 50% more enmity). Flash is pretty poorly understood because it doesn't provide explicit numbers, but it's not nearly as bad as you make it out to be and benefits from a fair deal more than you give it credit for.
That aside, I agree with you on the relative uselessness of Flash, though I probably think it's less useful than you believe since I don't even bring it for the 3 cases you brought up.
