[As far as "Batman beats the Martians" thing ...]
Yeah, but look at how the scene is staged. Batman has already defeated A-Mortal. Fine, he caught A-Mortal with his pants down, but that which should put every remaining Martian on the highest of guards, because they know 1)he's a great detective and 2)their own intense vulnerability to fire.
Instead, they permit him to spout tough guy lines and explain how he deduced their Martian origin (something he's done which they should have already figured out, since it's the most obvious way he defeated A-Mortal). Then they permit him to light a match. One of them is even arrogant enough to say "That little flame can't hurt us."
However, in the time she said that, any one of the three Martians surrounding Batman could have rushed him, and torn him to pieces. Or stayed still, and Martian-visioned him to pieces. Or used their telepathy to tear his mind to pieces. Instead, they allow him to flick the match into a ring of gasoline (I won't get into how being inside a ring of gasoline is not a healthy place for a human to be either).
But! Let's concede them the arrogance. Any one of the three could have caught the match before it reached the gasoline.
But! Let's concede they were afraid for a moment, and didn't act.
They had been, a few pages previously, shown to be able to almost keep pace with Wally West. They can still outrun the chemical reaction of the gasoline before it reaches a level to produce large, disabling flames. They're watching a small fire fall, and then gasoline oxidize, for a subjective hour, yet do nothing.
This is why Flash/Superman-level superspeed is sort of a broken power. At least, it's very difficult to plausibly write about, unless you give everyone else the same ability.