It's normal. Every single iPhone and iPad I've owned since 2010 have had the slight loose/wiggly power and volume controls. To test if it was normal I checked 3 different Apple suppliers and Store's displays, (Best Buy, Simply Mac, Apple.) Then checked and compared all my own iPads:
Air 1, Mini 2, Air 2, Mini 4, iPad Pro 12.9" 1st Gen, iPad Pro 9.7", iPad Pro 12.9" 2nd Gen. iPhone 4, iPhone 5S, iPhone 6, iPhone 6S, iPhone 7.
It is absolutely normal to have a slight give/looseness, years ago and even just last year I asked several Apple techs, Reps on the phone and in-store, Best Buy and Simply Mac reps, and then checked with a good friend from Apple, and all confirmed without doubt or delay that it's completely normal.
Kallum.