"Our website has a responsive design, so we don't need an app"
I don't know if load times really are 8 seconds, but yes, native apps are most of the time faster and yes, they do offer a better user experience. I think part of the problem is that we are so used to browser tabs. Right now I have 10 tabs opened, and even more on average. For me, tabs don't work as well on mobile as they do on PC. Yes, you have tabs in Chrome for phones, but I prefer the way they are displayed on tablets, in a more desktop like way.
IMO this would enhance mobile browsing, but it doesn't solve the load time "problems". The author of this article seems to be a fan of in-app browsers. I totally dislike them, as these don't have tabs at all. Since its launch I've been using Link Bubble, which solves, especially in combination with TapPath, a lot of the loading problems. While scrolling through my Twitter feed, I can single-tap a link to have it opening up in a bubble, double-tap it to immediately save it to my Pocket reading list and when I tap three times it opens in Chrome (obviously this is all customizable). This might even be better than Facebook's new Instant Articles, because most of the time I don't even have time to read it when I come across it.
As a news site however, I think it's better to have a native app, which might even allow offline reading. Although there are alternatives like Google Play Newsstand and Flipboard and if you use it the way I do, even Pocket.
Whether or not you should join the Instant Article program, I don't know. It's a bold move however, but I will probably turn it off, if I used the Facebook app at all.