Proprietary membranes from major brands can absolutely hold their own against GORE-TEX—some even rival its performance at a lower price point. The North Face's Futurelight, Patagonia's H2No, and Marmot's MemBrain are all solid options that keep you dry and breathing comfortably on the mountain.
The catch is that performance varies widely between brands. One proprietary membrane might offer near-GORE-TEX waterproofing and breathability, while another cuts corners and leaves you damp on a stormy day. That's why it's worth looking up reviews for the specific membrane you're considering rather than assuming they're all equal.
Proprietary membranes often shine in value—they typically cost less than GORE-TEX while delivering strong performance for most resort and side-country riding. If you're not pushing into extreme backcountry conditions, a well-reviewed brand-specific membrane can save you money without sacrificing comfort.