I just noticed this myself today but from my feeling it has been like that the whole time but I could be mistaken. I noticed it after I finally sorted out the whole SD card business.
Using the back button works indeed a bit faster. But seeing the delay is always the same, if I have to guess this is done intentionally for whatever reasons. Style, loading in the background I dunno.
What I just do is to use the show running program button all the way to the right. Most likely, the app you want to use is in the background and that way you can reach it quite quickly.
But of course, I’d also like it to behave instantaneous. So if somebody has any ideas on that one, I’m all ears as well…