spoiler The changelings and Sirens being rivals?

[SunsetBaconDrive 169]

After watching the finale I am just having racing thoughts of Chrysalis who she possibly knows other than ponies. Head canons are meaningless outside of my imagination... But shouldn't logic dictate that the changelings and sirens had to compete for energy of prey? Have Chrysalis and Adagio scrapped before? Sirens look so big, they should be able to eat 5 changelings and think nothing of it(RIP Willy Wonka) 

 

Chrysalis and Adagio are almost the same character... Chrysalis has an army, while Adagio just has her two lackies she drags around behind her.