The delay is occurring because you are having to use so many cloud to cloud interactions. I am actually surprised you only saw a 10 sec delay.
If you want this to work your best bet is going to be to replace some, or all, of your devices so that they can talk to each other on the same platform. Whether that is all xiaomi, melross or devices that will work directly with Smartthings. As long as you have to use so many different services to make your lights turn on your going to have a long delay.
Everything I have talks directly to my V1 Smartthings hub but, being that it’s cloud based, I will, on occasion, still see a 1-2 second delay from the time a motion sensor or door opens until the light comes on.
On a positive note, you learned a lot getting this project to work!