SmartThings is generally used for automation and triggering things to happen when other things happen, etc.
Wemo can do this too, but it’s only dealing with about 3 compatible devices versus potentially 1000’s of devices that are z-wave, zigbee, lan, etc.
SmartThings is a more complex system than wemo with more variables in the mix.
As for why your timers aren’t firing, I’m not sure why…
Right now I have not had any issues with things going off when they should.
Also, the batteries in the hub are a fail safe to protect the device and information most likely from power related disturbances and interruptions.
But they aren’t full proof obviously… if your modem goes out, your router is probably down too which would render your Wemo devices useless as well in that situation.
In my home, I have an APC Battery Backup system where my server, hub, router, modem etc are plugged in to. So if power is out, those specific devices stay on… probably for about 15 minutes or so. But if power is completely out, again, your wemo devices won’t work either since they aren’t battery powered… kind of doesn’t matter any way.
Also, in a world of interconnected cloud services like IFTTT and any external influencing services that people want integrated, having a centralized “API” hosted by SmartThings outside of your hub helps ease connectivity and authentication to these services. The Hub is getting to be more of just a “portal” / “modem-esque” device for z-wave devices to communicate with the SmartThings Central API (they add the word “graph” to it as if they are trying to gain cool points amongst developers? Not many companies use the term Graph… in fact Facebook is one of the only ones that really use it… That’s beside the point…
Either way, that’s where the dependency on having a constant internet connection comes from. Also since Wemo devices don’t have a hub, really no way to automate it without some sort of external influence such as your iPhone or Android Device firing off signals.
If all you’re looking to do is switch a light bulb on and off, SmartThings is going to feel like overkill.
But if you want the ability to expand later and not worry too much about if something is compatible or can be MADE to be compatible with your hub, then stick with it - it’ll get better.