In short? No.

Anyone who regurgitates the definition of the format as it being 'good' and 'flexible' and touts its 'versatility' probably not even using it in their own work and they're just reading a description of it from Wikipedia. It's a format that sounds good on paper but in actual use for your typical 3D artist can be a pain. Don't get me wrong, it can be powerful. It requires a lot of organization. NVIDIA's Omniverse is the only platform I think that is recently trying to forcibly adopt it, however, you can author models in FBX/OBJ/GLTF and bring them into USD in that software. But again, that's in that context. I only seeing it being useful to large animation studios with proprietary software pipelines, where large-scale organization is absolutely needed across hundreds or thousands of individuals who will have a hand in something. But imagine the file size... In a strictly Augmented Reality context, I can think of several limitations and headaches the format provides. GLTF/GLB is a far better 3D format for web usage. Apple has repeatedly refused to play ball with everyone else on the web. Just look at how poorly Safari is supported, and most developers use Chrome. GLTF has had far more extensibility. KHR extensions and Draco compression higher fidelity and smaller file size models to be viewed with a model-viewer and augmented reality. Things like glass refraction, sheen, etc, and other fancy shaders can be seen on models on the web, packed in an easy-to-transfer format, across multiple devices. Artists can use multiple UV channels for specialized maps like Ambient Occlusion and Normal Maps, and tile detail maps on another channel for optimized use of texture resolution. USDZ does not allow any of this. Not only that, but USDZ isn't even compressed despite being a 'zipped' format. How useless. So once again, Apple has decided to keep a stagnate walled garden. It is incredibly frustrating. If I'm creating AR models/products for clients, they appear vastly differently across iOS and Android devices because of Apple's limitations. This should not be the case. There's no point in having what you would call a 'standardized' format when it cannot be used as standard across different devices.

Without seeing exactly what environment you're testing your files in/with, it could be a multitude of things: The simplest explanation I can think of is the environment lighting could simply be different/darker. The color space or texture maps were affected (not likely though). The material shaders could've been affected during conversion. Texture maps have a multiplied factor from 0-1, or black to white. You can adjust this in some gltf editors. It could be possible that the conversion is multiplying the factor on the color maps with a value less than 1 (so a grey or darker color).