It's well-known by now that Heyman has been extremely active on his brand, while Bischoff has only been working periodically, and it's believed that the latter will not start making changes to the product until October.
On Oh, You Didn't Know (h/t Ringside News) Brad Shepard explained the differences between Heyman and Bischoff's jobs up to this point. Shepard said that the former "is involved in the creative aspect."
Shepard also explained that Heyman has been in the WWE "forever," whereas Bischoff has "a big learning curve," since he hasn't been in a big executive role like this for "decades." As Shepard pointed out, Bischoff's long track record and experience will lend a huge helping hand to WWE. It's just a process of getting him back into the mix.
Heyman has already brought major changes to Raw; in his first episode of Executive Director, we saw Bobby Lashley and Braun Strowman crash through the LED screen - which set off fireworks backstage. Heyman brought back the hardcore element of wrestling, and he's slowly been adding more doses of the Attitude and Ruthless Aggression Eras ever since.
Even though Bischoff hasn't gotten his hands on the SmackDown show yet, we've already seen major changes there as well. WWE began pushing Kevin Owens as a top babyface, and he's gone to war with Shane McMahon and Dolph Ziggler. The SmackDown product has already improved immensely, and the sky will be the limit once Bischoff assumes control.
What This Means
Heyman has been around WWE for several years, managing Brock Lesnar, so it obviously makes sense that he was thrust into his Executive Director role right away. Bischoff hasn't been with the company for over a decade, so it's obviously best for him to learn the direction before taking over. But once he does, SmackDown promises to reach another level under Bischoff's leadership.