Yes, it has improved response time incrementally but noticeably, for me. Button presses via Home app are truly instant for every single accessory, and now voice commands via HomePods are only a few seconds (maybe 2-4 seconds if I had to guess...and they are instant when using an iPhone for commands).
The key is to have a strong network. I have Unifi networking equipment with 3 hardwired APs throughout my home. Dedicated SSIDs - a 2.4ghz only with WPA 2 for legacy devices, and then a 2.4/5ghz mixed with WPA 2/3 mixed for the more capable devices. Tune the power of the APs, set your channels, don't be greedy on the channel widths.
If you do all of this, your HomeKit system will work flawlessly. I have 120+ devices with 60+ automations that range the spectrum of all accessory types and everything has fantastic reliability and response.
The new HomeKit architecture just made things slightly better.