Hi there, as I noticed not many people actually read 'some another post' in already existing discussion so will try bring this up here.
I have tried disabling all addons and set graphics to minimum as well as both with no luck, unexpectedly found out that if I'm turned in a way my appearance cannot[not able to] be suppressed with other outfit, then I again have no delays with bar swapping. This occured in quest in Glenumbra A Step Back in Time. As wanted to try something similar-done quest for skeleton polymorph.
With polymorph on the swapping delay problem is gone. Ugly as hell, but works even with addons on and almost-full-as-always graphics. Please try it out and say if it works not only for me