Mostly harmless… To quote Douglas Adams (THHGTTG was 42 at the weekend!)
There have been many instances of malware getting through the Play Store. But these are obscure apps from unknown publishers, in the main, I think there was one case of a well known app producer’s certificate being abused.
But, in general, as you say, if you stick to Play Store (and well known and trusted apps) and don’t root or side load, there is little need for AV - I’d also suggest not using Chrome, but there again, I’m a paranoid Infosec’er.