Mitts are okay, but a dead loss as soon as you need to do anything fiddly, like tying knots or placing screws. You're right on the less seams thing though.
I've visited the Gore test centre and they have machines that attempt to replicate real life wear by putting the boot on a flexing artificial foot and bending it repeatedly in water. I have absolutely no doubt that the Gore membrane is waterproof and, as new, the inserts in boots and gloves are waterproof. What that doesn't tell you is what happens in the real world where grit gets into boots and rubs against the liner (Brasher use leather linings to avoid this btw), water runs down trousers and wicks down socks etc and, of course, wets out.
For what it's worth, my experience is that nothing will keep your feet or hands dry in typical UK deluge conditions, it's just a question of how long it takes for the water to get in or condense on the inside. In a way, the gear companies have created unrealistic expectations with some of their advertising.
The other thing that the mags don't seem to put across is that breathable clothing works best when it's cold and dry outside and warm and moist inside so there's a temperature humidity gradient. That's what you tend to find in high mountain conditions - viz, Alps, Andes, Himalayas etc - but it isn't the case in the UK most of the time where we tend to have a damper, warmer cold, so a garment that works well at altitude won't be anything like as effective in, say, Scottish winter conditions. Cue stuff like Paramo and the pile-Pertex variations which can be more effective over here. Worst example seems to be windproof fleece which simply ends up feeling clammy very quickly in the UK - even the best of what we've tried (MHW's Windstopper Tech Jacket) still doen't quite work over here.
