Heck yeah, I’m mad. I like Sonata, specifically because we both like tacos, but that’s it. Besides loving tacos, I don’t really like Sonata.

I’m not mad at all. Though I do respectfully disagree with OP’s assessment.
 
I like Sonata, but I cannot ever declare her best pony/whatever. Rarity still exists, after all. So does Sunset Shimmer.

@martianmister  
too frightning for the youngens.

It’s really weird because their toys shows them as ponies.  

raindow rocks i am dispointing <:/

@Background Pony #9386  
Or, the best siren.

Sirens are semi-ponies. Sonata is the best semi-pony.

@Background Pony #FA74
 
“then why do they gain pony-like ears, extended ponytails, and translucent fin-like wings when they transform”
 
Their ears can be said to be Siren like and longer hair has no real connection to actual ponies besides just being a feature of transformations.
 
“instead of just going siren”
 
Same reason Twilight gains her ears, ponytail and wings instead of going full Alicorn. No one changes into their Equestrian form.
 
“isn’t there siren form there “true power” then if they are sirens??”
 
Sirens are their form in Equestria, as shown in the book Twilight uses to identify them. The projections were just projections just like the Alicorn that defeated them was a projection. They can’t be Sirens in the human world anymore than Twilight can be an Alicorn but they do have access to magic.
 
“and others say the siren form is just a Astral form where they can output greater power”
 
Twilight’s book shows them being banished as sirens, I doubt that they are anything but in Equestria.
 
More information is forth coming in a few months when IDW Comics will do an issue exploring their origins. Besides that it is pretty clear that they are Sirens in Equestria and humans with Siren magic thanks to their gems in the human world.

actually, what is the exact truth?
 
because of this i went ahead and searched towards it, i’m reading multiple sources and it’s a bit vague at best.
 
some sources say there human in EG realm and Siren in MLP realm while in other sources i read text suggesting there human form isn’t there true form in EG? if so, then why do they gain pony-like ears, extended ponytails, and translucent fin-like wings when they transform instead of just going siren, isn’t there siren form there “true power” then if they are sirens??
 
and others say the siren form is just a Astral form where they can output greater power with (or something along that line)… from which you would say it would almost be the case regarding whats happening in the movie..
 
so… is it said anywhere what is truely the case? or are we just gonna guess forever.

My associate and I respectfully disagree.
 

Why would I be mad for you telling the truth?