If the cavalry is going to arrive to save the day, they should do so in an exciting and dramatic fashion. You want to show off that they can achieve what the beleaguered heroes couldn't manage on their own. What better way than to have them pull off impossible trick combat manoeuvres?
Commentary by memnarch (who has not seen the movie)
Whoa! I guess Rey completely disappeared from the area for a bit if she's on the Falcon now; I wonder how she managed to pull that off? Hopefully something more comfortable than that space pod coffin she took to get to the First Order from the Falcon previously.
Anyway, now that the Falcon is here, I imagine things will go much easier for the Resistance. Okay, not easier exactly, but it won't be a curb stomp any more. I'll predict that most of the skimmers get blown up in the end and the Resistance base takes at least one major hit, but all of the First Order vehicles get exploded. Hm, except for whichever one has Kylo and Hux on board; I don't think we can afford to lose any more major villains at this point in the movie.
Transcript
GM: The First Order wins initiative.
GM: Three PIEs lock onto <roll>... Rose’s skimmer.
Rose: I try to evade!
[SFX]: Pow! Pow! {the PIEs fire at Rose’s skimmer}
[SFX]: vreeeeooooowww... vreeeeooooowww... vreeeeooooowww...
[SFX]: skkrrkkssshhh!
GM: Suddenly a single shot blasts all three PIEs from the sky!
[SFX]: Pow!
[SFX]: Boom! Boom! Boom! {Now those PIES have no room; And as the Falcon takes flight; They all got caught in its sights}
GM: It’s the Falcon!
Chewbacca: I daresay, we have timed our arrival at Crait to be as optimally facilitatory and dramatic as possible.
Rey: And I get to fire big guns!
[SFX]: Pow!
[SFX]: Kaboom! {Rey fires the Falcon’s gun and destroys another PIE}
Poe: Wait. They get to save the day?
Chewbacca: Yes, but we have no intention of dying while doing so.
Poe: Oh. That’s all right, then.