When I first wore Rohan clothes they were cutting edge lightweight gear using new fabrics and esoteric styling. When the company was sold they drifted to a more conservative mind set, becoming increasingly oriented towards travellers rather than walkers.
Even so they have been early adopters of certain fabric technologies like silver impregnated base layers. In the latest catalogue they have a couple of items that will interest lightweighters.
Their Elite trousers weigh just 200g. Their old Essential trousers (which I have) weigh 369g. Montane Terra pants weigh 354g. So the Elites compare favourably, although they are rather expensive at £80.
More reasonable is the Ultra Silver T base layer at £30, weighing a measly 60g. My lightest base T is the Berhaus X-static at 122g. The Montane Terra T is 130g. If the weight is true, then they are half the weight of competing base layers.
The Windshadow jacket also looks interesting but is a bit heavier than competing wind shells at 220g, but has more features.
If you prefer to be a bit more conventional in style, then Rohan is always worth a look.