The best decision that The Flash made for season 6 could be repeated in 2021 when the CW series enters season 7. Season 6 differed from past seasons by splitting into two separate stories, with each one having its own main villain. This was the first and only time this has happened on The Flash.
The first half of The Flash season 6 dealt with Barry Allen (Grant Gustin) dealing with his impending death in Crisis on Infinite Earths, while at the same time struggling to defeat Ramsey (Sendil Ramamurthy), a scientist who became a murderous villain in order to avoid death. The second half, which took place after Crisis, focused on the aftermath of the event and provided Barry with two new problems: the unexpected death of the Speed Force and a new enemy in the form of Eva McCulloch (Efrat Dor), a gender-swapped Mirror Master. For a while, Barry was focused on other concerns and was unaware that his wife, Iris (Candice Patton), has been a prisoner in the Mirrorverse since the end of the midseason premiere.
Cutting the season in half and giving the show two main villains rather than one served as an interesting formula for season 6, and it could be used again in season 7. As for why it happened in the first place, the reason could be connected to Crisis, considering that it was so integral to the plot. Based on its importance, it made sense for the season to have a pre-Crisis story and a post-Crisis story, so that they could relate to Barry's problems on a personal level. This was certainly the case with Ramsey, whose determination to live tied in well with Barry's decision to accept his death as inevitable.
Since Crisis is over, reusing season 6's villain format may not be necessary, but it worked so well that the producers and writers may decide to go in this direction again. Having two stories didn't hurt the show, nor did it feel that The Flash wasn't giving each plotline enough time to tell a complete story. In fact, it felt right for the show and helped The Flash to avoid some of its usual mistakes. In past years when Barry had to focus on one villain for an entire season, Barry's numerous and consecutive failures to catch the villain tended to become repetitive. This was a problem that plagued season 5 in particular, as both versions of Cicada always seem to escape from Team Flash. This was fixed in season 6. Since each story was only half a season long, Barry's conflicts with Eva and Ramsey never felt like they were being stretched out.
Due to the production delays, The Flash season 7 may be a bit different, since being cut down to 19 episodes didn't allow season 6 to resolve its Mirror Mistress arc. That means the season may have to use up at least three episodes (three more were originally planned for season 6), but the remainder of the season could be devoted to new challenges for Barry to face. The rest of the first half could see Barry dealing with a revived Reverse-Flash or the real Godspeed, and the back half could pit Barry against a new adversary.