On Plasma 5.0.1, I can start an application, and it nearly never gets the focus. Focus Stealing Prevention is very low, but it still does not work. Even disabling it does not help.
also see bug #110543 and https://git.reviewboard.kde.org/r/110919/ (won't apply to 5.0) *disabling" FSP ("none") should however work - it bypasses all considerations and just passes the window the focus. *** This bug has been marked as a duplicate of bug 337798 ***