qwertyuiop1998
The Vampire
Well, Here is my two cents of this scene
First, We can see Synmar was using Yellow Energy when BA attacking him
https://ibb.co/t2pKsD3
Next panel, BA using and cover Synmar with his lightning
https://ibb.co/mSbWcz1
Synmar then immediately flying to Naomi while JL barely found their footing in no condition to fight
https://ibb.co/z6b6nrN
Now look closely, the lightning energy that previously covered Synmar body begun changing into Yellow Energy and Naomi wasnt doing any attack
https://ibb.co/zmy6vgz
Then an explosion of Yellow Energy happened, blowed BA away while Naomi still didnt look like she was attacking
https://ibb.co/QrDHVcs
And then Carver came in and said in this dialogue, "It" was referring to other JLers attacks
So lets move to the next panel, Here it stated
"Naomi sees other leaguers from past and present Descending on the hall, Pouring in from every direction
"Justice league! All members old and new!......We're taking the fight to him!"
So obviously, Other JLers moved at this location only moments ago, And now Batman pointing out who is the enemy. And of course these JL members attacking Synmar before is very unlikely
https://ibb.co/VTrxjg2
But most importantly is the statement of Flash
"I think this Synmar's absorbing and Transforming energy into more energy"
https://ibb.co/K2kSY9P
Finally, We see Synmar covered in a yellow energy which much like the energy of explosion that blowed BA away
https://ibb.co/HC2zsvS
So is "it" referring to the lightning energy that Synmar was being covered that we clearly see, Or is referring to JLer's attacks which we didnt see in these scans?
But all in all, whether you want to interpret "it" was referring JLers attacking him or "it" was referring to the lightning energy that Synmar absorbed and transformed. This scene doesnt necessarily show BA did better job than entire JL combined as I and DS pointed out.