If your bulb cannot support certain effects natively (like blink and flash) then attempting to emulate them with on/off commands is limited by Zigbee’s communication speed. For every command propagated to the light via the mesh network, there is a reply from the light acknowledging receipt of the command. These transactions take a finite amount of time. The shortest possible interval is simply an on command immediately followed by an off command. That’s what you tried and concluded was too long. It’s hard to imagine how on/off can be reduced.