Earlier quoted context omitted.
I don't know what your Z-wave setup looks like, but all I've got are GE smart switches and GE smart outlets, controlled with Home Assistant using an Aeotec Z-stick. It works flawlessly with zero noticeable delay, 100% of the time. It sounds like you've either got some bad interference or bad devices.
So much of one's experience depends on the z-wave hardware and it's not obvious at all which brands or products will be more reliable or better than others. My network is a hodge-podge of different switches and outlets, but mesh networking means it's easy to poison the network with a bad implementation. And then good luck finding the offending hardware.
Up until this past year, every single ZWave radio was made by the same company. They are now allegedly certifying third parties but I haven’t yet seen anyone announce that they’ve achieved that certification. It’s possible to build a crappy ZWave device, but the radio and network side should be solid, even on crappy devices.