please help me to decide: should I use AMP or should I turn it off?

Personally I stopped using amp pages. Sure, it speeds up your site a little bit if it's a blog but I feel they're a worst user experience than having your regular site load on a faster server.

The reason you're most likely seeing a high bounce rate because if someone is reading on Google News they can scroll though though the amp articles by swiping.

Metrics that you are analyzing are percentage, It means if integers values decreased probably percentages will increase. So, you need to understand what are website long-terms top ranking. If you provided information contents without a call-to-action or your blog user experience is no good, probably your blog wil keep a low performance.

If you notice that AMP is causing conversion decreases, I would have to suggest avoid using it.

You do not need to rely on AMP to improve mobile page rank.

Try doing things like keyword-optimized internal linking (perhaps via a Related articles section at the end of your posts), and mobile footer optimization. Be sure to use structured data (Schema) wherever possible as well.

Remember to build quality backlinks to each page you hope to rank.

In my experience, many sites do benefit from using AMP for faster page load speeds, but usually at some cost to conversion.

If any questions come up, shoot me a message.

Blake