Why should wearables be less complex? Sure, what on the market now is, but I see no reason wearable systems couldn't be more complex than smartphones and more convenient
Wearables are necessarily less complex. If it's strapped to your body somehow, it's less convenient to manipulate. an Iphone 6 plus on an armband isn't a wearable, it's a phablet you've anchored to your bicep. A Nexus 6 on your wrist is a Nexus 6 you can only use one hand on. Complexity requires dexterity. Wearables are less dextrous than non-wearables. Pocket watches had latching covers to protect their watch glass because opening a watch glass cover was a natural, easy motion when the pocket watch was in your palm. Wristwatches don't because it's cumbersome and inconvenient, even though wristwatches actually need more protection than pocket watches.
Wearables need to A) look good. Phones aren't something you wear. B) overcome the stigma against wearing a large screen. C) last long enough to not be annoying or go dead midway through the day. D) work in bright sunlight, survive harsh environments, etc. I honestly don't see watches replacing phones. Not now, not ever. They will become a very good tool to help use of phones, but I can't see it going further than that. It will become a "Tracker" that you can see and monitor your day and life through, where the phone is a "portal" to the internet and to other people.