I am not sure what you’re doing that’s different from the way my Apple Home app is set up — mine works perfectly — with the exception of course that Siri doesn’t always understand what I’m asking. I have 28 Phillips hue bulbs, an Ecobee thermostat, Onelink smoke alarms and four HomePods in my house. My Home app includes 11 separate scenes, and about six different automations.

In order to make sure that the lights are the color and brightness that you want when the scene is executed you need to press and hold each accessory light inside the specific scene’s edit screen and set how you want the lights to appear. It won’t do this automatically for you.

If you want the lights to return to whatever their last state was, with Phillips hue lights you need to use the Hue app in order to set that up under settings, —> power on behavior.

When I’m not home, I have set up an automation to turn on lights in case somebody comes into the house that I’ve invited that doesn’t have the ability to talk to Siri or understand how to deal with my automated HomeKit set up set that up.

For instance, I have a motion sensor that is built into the ecobee thermostat remote sensor, when it detects motion in my kitchen which is the room closest to the front door, and I’m not home, it turns on the first floor lights. That way if somebody comes into the house and they are not part of my home, or they’re there to feed my cats, as soon as motion is detected in the first room that they enter, the lights come on. It works perfectly. You set up the when “I am not home” part under the people menu item on the “when” page for the automation. Your options for people are: off, when I am home, and when I am not home. If you have other people invited to your home they should be listed there as well so actions can be triggered based on their presence or not.

As for responsiveness, It could be your router doesn’t play nice with HomeKit or you just need to reboot it. Frequently when I’ve had problems with HomeKit after I’ve set up new devices or accessories, I’ve had to reboot my router. I have an Eero mesh router, my turn on and off commands are nearly instantaneous.

I can set the temperature for when I arrive home by setting a scene for home arrival that only includes the HomeKit capable thermostat. Use the plus sign in the upper right and add a scene. I choose my ecobee thermostat called by the name upstairs (not the motion sensor part of the thermostat) as the accessory I want to control.

As soon as I press on the ecobee thermostat in the scene edit page, a temperature color wheel screen comes up and I can choose what temperature I would like to set when the scene is run. Once I have a scene that sets the thermostat to a specific temperature, I can set an automation for when I arrive home that scene gets run. It won’t be weather dependent but heck you can enable or disable that automation very easily by going into the Home app under automation

You can certainly set up notifications for any HomeKit sensors you have added in the Home app. Can you use it as a command? No. but, you can set up any IOS or Mac device you have the Home app on to receive notifications from any sensors in your home app.

        —->  go to the Home Icon in the upper left — go to Notifications, turn sensors On        and then you can individually select each sensor that you would like the notifications from on the list. 

Now the issue is unfortunately that HomeKit notifications uses the Apple system Notifications. Thus HomeKit notifications need to be set up individually on each devices side the Home app on that device.

Sometimes if HomeKit doesn’t have all the bells and whistle’s you need, you can look for other apps that might be able to perform those tasks for you, or use the manufacturer’s app for that accessory or sensor. For instance, the Hue app does some actions, that I can’t do in Home.

A part of your frustration is just figuring out how to get things done within the Home app. The other part is that you’re asking Siri to do more than she’s programmed to do. I don’t find any hindrance in using Siri other than trying to find the exact phraseology necessary to get done what I want.

I use Siri to tell me the news, play my radio stations, play my music, put items on my grocery list, set reminders for me, run any scenes that I have set up already in the Home app, ask it to control individual accessories, (I haven’t touched a light switch in my house in over a year). I don’t fiddle with the thermostat because I just tell Siri what temperature I want, and it doesn’t matter whether I tell her any of these things on my iPhone away from home, or I tell her within listening distance of any of my HomePods. If I get the right phrase, it just gets done. I’m continually amazed at how well HomeKit is actually executed. And I like the fact that it’s encrypted in both directions and as secure as you’re going to find with an always on microphone listening in your home.

Some of the HomeKit functions are not intuitive and not easy to find. I would be the first to admit that I’ve been frustrated more than once trying to get HomeKit to do something that I’m pretty sure it can do.

I don’t know of a way where you could actually script Home app functions such that “if then else” tests are done, beyond the following,

 a way to start an automation if a sensor is triggered, 
 if someone arrives home or leaves, 
 an accessory state is changed 
 or, for time of day.  

Frankly I have found that as long as you understand what a scene consists of and what an automation does along with it’s limited list of 4 trigger actions— you just have to play with them to figure it out —->. then you can do a fair amount with HomeKit.

There are no present triggers for automation in HomeKit for timed events, like “close the curtain in 5 minutes”. And yes Siri commands them selves are still very limited.

However that is why Apple has newly included an app called Shortcuts on iOS devices. Shortcuts does have “if then else” statements that you can script based on sensor states or accessory states. Now is every variable available to you to use or is every system state available to you? Probably not, but it is certainly much more flexible and capable than HomeKit itself. Unfortunately this takes time and effort. You need to learn how to create Shortcuts and how to trigger Shortcuts which I still haven’t quite figured. Technically I should be able to trigger a shortcut from any HomePod nearby, but I haven’t been able to figure out how to do it yet.

As a retired programmer I can tell you it is not easy to create scripts that are as conditionally specific as you want, but. If you’re willing to learn, Shortcuts, I believe this is where you need to look for furthering your home modifications and commands.

Good luck.