Getting a book off the shelf. Firstly my memory's crap - it's a V term, not a V^2 term as I claimed earlier.
Working in the normal plane, this shows in response to a sharp edged gust that the change in normal acceleration is...
delta_Nz = 0.5 x rho x V x (lift curve slope) x gust velocity / wing-loading.
(Intuitively, response will be much the same in the other axes.)
So high wing loading = low gust response, that we can all bear out with experience and just looking around at the world aircraft fleet. But...
The issue here is that whilst you're quite right and higher speed gives more control, that same higher speed gives the gust more to work with. Multiply aircraft speed by gust strength, and you get something linearly proportional to the aircraft's motion response.
So whilst the control authority should also improve - if it's adequate anyhow, you're giving yourself more to correct by flying at higher speeds. I know it's anti-intuitive, but the maths seems to work, and it seems to work also on the smaller aeroplanes I fly.
Regarding FAA and EASA - I've not yet seen any *science* from either justifying the "half gust" amendment to Vref. If I'm wrong - which is entirely possible and wouldn't be a first - I've not seen proof of it yet.
That you've not come a cropper using the method you have could mean one of a number of things. One is of course that I'm wrong - another is that there's enough margin in everything to mean that it doesn't matter as much as we think - another is that gust response and control authority scale about the same (which probably is true) that they pretty much cancel each other out.
G