I am working with a fresh whole-house install - first Z-Wave setup, all 700 series as follows:
1 - Hubitat C7
25 - Zooz Zen77 dimmer switches
10 - Zooz Zen76 on/off switches
3 - Zooz Zen34 remote switches (2 active, 1 spare not setup)
8 - Minoston MP31Z on/off plugs
5 - NewOne N4002 dimmer plugs
I have a 2 story w/ full basement about 3600 sq/ft
I located the hub in the most central location of the main floor I could and worked from the hub out. I initially started with the plugs since it was quicker to put them in place, I joined them to the hub then proceeded to install the switches (and those 2 battery remotes last) ... I set everything up using smart start with QR code so S2 security authenticated thinking this was the ideal configuration.
A few weeks passed and I was not happy with the response times. I was hoping maybe things would settle in or running repair might improve but it never did - I didn't install any watchdog service or anything to measure, just obvious. Mostly noticeable using Alexa and some physical switches with virtual 3-way and 4-way when not connected directly to the load (FWIW - I've used the mirror app and direct association for the virtual ~ doesn't seem any different either way so sticking with mirror app for now).
Over the weekend I reset everything (full reset on the hub, exclude w factory reset on the devices) and rejoined (with switches first this time since they were already wired, dont know if it that matters) then plugs, then the battery remotes. This time I did everything with no security. I can say my experience is very much like yours - response is markedly improved. Even with Alexa it is now turning on/off devices as soon as I utter the last syllable!
edit: forgot to mention I had already updated the hub to latest release / z-wave firmware before reset, also zigbee disabled before and after since I'm strictly using z-wave
edit 2: mirror app was getting flaky on me - went back to direct associations
