Yes, content is king. And it doesn’t matter if someone is visiting your mobile site or desktop site. They are looking for specific information or a specific product, so you better make sure content is the same on both. It’s common use to hide some larger images on a mobile device or put some more content behind tabs (which is OK for Google, don’t get me wrong). It speeds up rendering of the mobile content, which will only help both users and Google. But the end result of that mobile optimization should not interfere with the end goal of your desktop site. It’s the same. So in regards to content, mobile parity matters.
My overall point in this is that having more content is better for SEO. Does your content answer the questions your clients are search for? Contact us for a free analysis of your sites content. If you are running a WordPress site and need a great plugin to assist, check out https://yoast.com/ . To get the most out of this module we suggest buying the premium version.