Why entire season when Naagin can kill all at once

So watching today's episode, the way Vish (in Brinda's form) killed everyone, why can't every Naagin just go and kill the humans like this.

Since the story has nothing new to offer in every season- always a revenge and a confusion with ML, its better the Naagin just go into each of the killer's room and kill them on a single night.

At least ye favouritism, finale me lead ko sideline karna, non sense story dikhana to band hoga.

Hina ko worst dressed and expressionless look me Sarvshreshth naagin batane se better hai don't make any new Naagin season please.

This season itself is a mess almost from start... 

There are so many side characters/youngsters...

But no proper villain. 

S1 only had human villain still they had some powerful pujarin n rings to tackle naagin

S2, s3 there r so many ichadhari creatures.. 

So that makes sense as why naagin takes that long to take revenge. 

But this season there is no proper villain itself.. 

They dont have any proper protection etc .. They just dragged some part... But missed some key points... 

How brinda n nayantata r swapped?! 

How come nayan became so selfish n obsessed with dev?! 

How Vishaka became negative suddenly at the end of s2?! 

Brinda's dad( pujari) knows that brinda is naagin from starting. Hiw?! 

And whom did he was talking to abt brinda?! 

Vish wants naagmani from dev. Then why killing his family in disguise of brinda?! ( of course to create MU... But she wants to kill him anyway then wats the need of MU?!) 

Lot of questions still... For got to add

It's the worst injustice Ekta did with Nia i.e.with Brinda's character.

Her character couldn't do to show her strength.

In S3,it was true SJ was sidelined but only thing which was satisfactory that was Bela/Shravani killed Sumitra and Sesha too.Although Sesha had been killed so many times😆

But here Female lead wasn't given chance to kill off her enemies