Both HomeKit and Alexa systems suck. I usually just open an app for either and select an action or routine I've already set up because voice commands are just too unreliable on both of those systems. Mostly I have routines set up to automatically set various lighting to specific parameters at certain times of the day and night, and that works fairly well with Alexa. I don't have many HomeKit devices yet, and given the issues probably won't expand them until Matters seems to be proven to work correctly.
Siri is stupid, and Alexa is argumentative and stubborn, and she wants to shove ads in your face!
I don't know your setup but Siri works well for me. I have a HomePod in each room. I set up a small number of scenes related to activities I routinely engage in like Good morning, cooking, watch TV, Work, Relax, Get ready for bed, and Good night. These have lights, TVs, speakers, smart plugs and the thermostat associated with them and some include Apple Music or Apple TV.
I go around the house and casually ask for those things and she always understands them. Outside of those scenes, if I need lights turned on or shut off, I simply ask to "turn on/off the lights" and Siri knows which room I'm in and turns on/off the appropriate lights.
I also have time based automations as well as activity based ones. If there's something in my work schedule, Shortcuts will turn on my Work scene if I'm home and it's not already on. When the sun sets, if I have nothing in my work schedule, my Relax scene kicks in.
Having devices outside of the HomeKit ecosystem will obviously complicate things and produce unexpected results. I just made sure to get HomeKit devices which also work with Alexa since I have an Echo Show in the Bedroom and Bathroom, as a bedside clock and getting ready in the morning screen, respectively.
Siri doesn't have to be that smart, it's a matter of setting up your home for how you live and how you'd like your home to act. Siri does make smart suggestions and understands natural language so the commands aren't too rigid. I've used this setup for years and aside from the occasional HomeKit bugs and delays in responding (almost always network issues), I've been pretty happy. The downside of this working so well for me is that I go to other people's houses and talk to the walls.
