Mesh networks don’t work that way because they are not continuous connections. By design, the messages are tiny and hopefully infrequent.
There are tools which will show you the message routing, but unfortunately smartthings doesn’t provide any of them. Some community members have bought an additional device and then used the tools that are provided with it, but most people won’t have to do that.
Z wave is a very robust topology. About the only two things you can do to mess it up are:
One) don’t have enough repeaters or
Two) add software that does a lot of polling.
But other than that, up to about 150 devices, you should be fine. There’s a hard maximum at 231 (Plus one for the hub), but you may start to see some slowing down above 150.
See the following FAQ (this is a clickable link). Start with post 11, then go back up to the top of the thread and read the whole thing.
As far as adding a second hub, smartthings does not allow you to add a second hub to the same location, so that’s not going to help.
