It would be great if repeat actions had an option to let the sequence run in parallel for each of the repeat runs.
The parallel option has been added for service calls in a sequence in one of the latest versions, but for repeat that doesn’t work. If you would have a wait or delay in the repeat sequence, they will wait on each other. To avoid that, you’d need to call another script.
How I work around this is call a script with script.turn_on so it doesn’t wait. Then loop the calls. It isn’t parallel per se but its pretty fast.
I acutally already mention that in my post 
But I would like to have everything in one script, and don’t rely on other scripts.
Well… I just got up and haven’t had my coffee yet. So there’s that! 
Haha yes! This is like one of the last things I really miss since migrating my automations from node red to HA. In NR any time I needed a loop I would use split and do everything in parallel, I rarely ever wanted processing of one item to wait for others to complete first. Now I can’t do that anymore