It's like anything, it's all about moderation.
If you're sitting looking at your phone instead of interacting with family, socialising with other people, or getting out and about - then no, they're not good for you. One of my friend's wives is completely addicted to her phone, to the point that I stopped going out for drinks with her because I might as well just have been sitting there on my own.
However, you're right in that they can be a great way to switch off and pass time. I have anxiety and I admit that sometimes in an evening I will spend time on a couple of my favourite mobile games, as it just wastes a bit of time that I would otherwise have spent worrying about things.
It might not solve the problem, but it takes my mind off it - and I am addressing it in other ways with my GP, too!
So, it's all about moderation and balance. But it's never the case that all gaming = bad or all gaming = good. I don't think people on here are 'anti-gaming' as such, more against their kids, OHs gaming ALL the time, or at least extensively. It's easy to let it take over, as it's very immersive, but if you're able to get the balance right then yes, mobile games can be great.