Zwave and zigbee are both mesh networks. They’re not designed for real time monitoring, but rather for tiny messages on low traffic networks. Sampling, typically once every 5 minutes or every 15 minutes. Also, there’s no forced sequencing, messages may bounce around the network a bit and can arrive out of order.
Most devices won’t report more often than every minute, and SmartThings won’t let you schedule more frequently than that.
Many zwave devices come with a fine print warning, “not to be used for medical devices,” for all these reasons.
There’s nothing wrong with mesh. The trade off for not having real time fixed routing is a network that is very cheap in terms of both energy draw and dollars per device. And highly resilient when any individual device goes offline.
But if you’re data greedy and you want real time monitoring, not sampling, you don’t want mesh. Choose star or tree topology, hard wired or cellular. Or WiFi if you’re ok with occasional drop offs. (WiFi is star topology, high data flow, forced sequencing. All good. But does lose connection occasionally.)
Or if you want to keep costs down and you want all the data but don’t need real time review install an inline recorder and upload the logs once a week or so.
So it just depends on what you want and are willing to pay for. Zwave energy monitors are fine for showing patterns of usage based on sampling. But not intended for constant monitoring and up to the second real time reporting.
Although a little old (2013) the following is a good discussion of energy monitoring systems.