From a writing perspective the point of Sera being Andruil is ...there's no point.
We got Solas because they wanted us to know him better before blablabla , it was always him but he was lying.
Now what's the point of having Andruil froclicking around saving peasents?
Andruil was a noble who was hunting other elves for fun and sports, she hunted Fen Harel and caught him and basically wanted to rape him ...
So first you have to change your tune about the Evanuris being trapped , and explain why or how Andruil escaped her fate.
Then you have to explain why Solas who really can't stand them walks around with Sera/Andruil , and don't notice it , and just let it happen.Later he'll say "Duh" one of many.
Then Mythal also being clueless , when she wants to probably torture them .
Then you have to explain Andruil complete change of personality , yes Sera has a bow , but Sera isn't a hunter , Sera has no patience , she pranks people.
Then you'll have to give Sera/Andruil a goal , because this was all dumb luck and you had two elven gods in the Inquisition ,it is really sloppy writing.
So why would Andruil just walks around , eating all the food , pranking people , getting married to Inqui , stealing stuff for her cabinet of wonder , baking cookies....?
The whole but Sera doesn't know Andruil is there , well if it's just to say "Hey Guys Sera had Andruil inside her , Woaw!"
There's like no point at all , and then you have to give explanation on the how it happened.
So why would any writer would bother with that?