I have also tried this with the same result, it either takes up to a minute to trigger a scene or it doesn't trigger at all. Like you said it isn't an acceptable level of reliability.
I hate that I have my Pico Remotes either synced to a Staples Connect to control my Philips Hue lights and another set of Pico Remotes synced to the Lutron Smart Bridge 2 for the blinds and then I have to use Siri for all the Eve Outlet switches. Not what I imagined a smart home would be like.
I emailed Lutron about this so they could hopefully open up their systems. I recommend other people voice their opinions as well.