Spoilers ahead for the February 4 episode of The Flash, called "Marathon."
The Flash returned to The CW with its first episode since the massive "Crisis on Infinite Earths" crossover came to an end with the death of Arrow-verse founder Oliver Queen and the combining of no fewer than six shows into Earth Prime. Showrunner Eric Wallace already confirmed that there would be some big changes to post-Crisis Central City in the wake of all the loss, and "Marathon" revealed that what is now the most senior series in the Arrow-verse really needed the crossover to rewrite its history.
At least, The Flash needed the "Crisis" reset in my book, and I say that as somebody who wasn't exactly thrilled that the Arrow-verse erased eight seasons of Oliver Queen's development in one fell swoop right before Arrow's series finale. But the Arrow era is over, and if The Flash is going to keep on running, then it needed the kind of reset "Flashpoint" promised but didn't really deliver. The Flash can't just go back to business as usual this time, and there are big consequences to the crossover.
Time travel won't fix what went wrong, and the Speed Force can't undo what was done. The Flash needed this, even if Arrow didn't. So why am I suddenly on board the "Crisis" train for The Flash? Well, for one thing, The Flash is still running, so it's time to make the best of things for the future. For another thing, "Marathon" provided some in-universe reasons why the Crisis was good for the show, if not for the characters.
The Flash Reinvented Its Metas
The Flash, with its speedster metahuman superhero, almost always relied on other metas as Barry's villains because the normal humans just quite literally couldn't keep up. Through the first five and a half seasons, though, The Flash was running out of new metas on Earth-1 and relying more and more on parallel versions of existing characters. Some of the scariest baddies weren't very scary anymore, and Team Flash had all the advantages with the stacked deck of meta heroes, technology, and resources.
Now, however, Team Flash can't count on all of the villains they thought they knew operating the same or even being the same person. Cisco had a whole book of bad guys who he had no memory of from his pre-"Crisis" consciousness, and the good guys had a hard time getting the win in "Marathon." Iris was injured, and if the timing had been even a little bit off, some of them could have died. Nothing is certain with metas anymore, and that's good for a show with a premise that was getting tired.
The Flash Got Rid Of The Extrapolators
I already mentioned the time travel, Speed Force, and universe-jumping as plot devices The Flash began to rely on too heavily prior to "Crisis on Infinite Earths, but one of the biggest conveniences that made things a little too easy for Team Flash was the extrapolator created by Cisco that let Team Flash pop out of nowhere and take the bad guys by surprise, whenever they weren't using it to jump between worlds.
In "Marathon," Cisco revealed that the extrapolator doesn't work now that the universes are combined into Earth Prime, even to jump from place to place in this one world. This meant Team Flash had to deal with the Villain of the Week without zapping Barry away from his mission to Lian Yu with Arrow's John Diggle to save the day. This episode was actually hard on the heroes, and that raised the stakes.
The Flash Didn't Kill Off Cisco
Before The Flash Season 6 even hit the airwaves, rumors circulated the Carlos Valdes was leaving the show. Although Valdes himself ultimately debunked those rumors, many fans have been on on Cisco Death Watch throughout the sixth season. If there is some truth to Valdes wanting to step away from The Flash or even The Flash running out of Cisco story, then "Crisis on Infinite Earths" provided a reason to write him out without killing him off.
Struggling with his inability to save Harry and others during the Crisis as well as his conflict over whether or not he wanted his Vibe powers back, Cisco decided to take a break from Team Flash and go on a journey to figure out the big differences between the former Earth-1 and the new Earth Prime. While this could result in a whole new batch of conveniences if Cisco comes back with a Bible of changes for easy reference, at least Cisco dipped out of Central City without dying.
The Flash Made Nash Wells Interesting
Although Nash Wells ultimately proved to be key to "Crisis on Infinite Earths," I kind of felt like The Flash was scraping the bottom of its Wells barrel with Nash. I love Tom Cavanagh on The Flash, but how was Nash supposed to matter once his somewhat inexplicable Pariah days had passed? Well, "Marathon" proved that Nash is suffering lingering effects from what he did as Pariah, has a connection to an alternate Allegra Garcia, and has been tasked with helping Team Flash in Cisco's absence.
Thanks to "Marathon," Nash Wells matters, and he won't be shoehorned in as a way to keep Tom Cavanagh around. On the whole, I think "Marathon" was a fitting way for The Flash to begin its tenure as the most senior series in the Arrow-verse. It spent some time with Barry reflecting on and mourning Oliver, with Diggle at his side to lend a hand. Is any of this to say that I didn't laugh at the image of Barry using Oliver's mask like Tom Hanks used Wilson in Castaway? Not at all, and I wouldn't be mad if that happened. But The Flash has made me feel better about "Crisis" rewriting history.
See what happens next on The Flash on Tuesdays at 8 p.m. ET on The CW, ahead of new episodes of Legends of Tomorrow, which is now the second-oldest series in the Arrow-verse, if we take into account the fact that Supergirl started on CBS. For more viewing options now and in the not-too-distant future, swing by our 2020 winter and spring premiere schedule.