Prevent delay between clicking on the task manager groups and the list showing up?

If there is a task running with a single instance/window, I can click it in the task manager (“taskbar”) and it immediately maximizes/minimizes. I think this is because I changed the “Delay focus by” setting in “Window Behaviour” from the default 300 ms to 0 ms. Good.

However, if more than one instance/window is running, and it thus becomes a “group”, and I click this group, it still seems to retain the delay by (at least) 300 ms. The result is a feeling that the UI is sluggish, when it’s probably just waiting deliberately before bringing up the list.

How can I make it appear instantly? Is it even possible? Since I click groups (and then click the right instance) a zillion times a day, it really adds up.

Please note that I cannot disable task manager grouping as a work-around because then there would be a constant mess of UXTerms being created and disappearing all the time.

If there is a way to specify which programs should (or should not) be grouped, that would help to alleviate this, but I’d rather have the lists pop up instantly when you click the groups.