I disagree. Ashe is one of the more serious characters, but she's always had this small element of playfulness to her. Her joke "no really, put that apple on your head ;)" has been there for a long time, and has an air of sassy confidence. So logically if they are expanding her VO they are going to add a bit more to that.
She has plenty of serious quotes, far more than playful ones. She laments having to fight certain characters (Sejuani in particular) and some of my favorite lines of her's are her long move lines, where she gives a prayer to one of the Freljord demigods. Its a handful of great lines that show her dedication and also give a little insight into Freljordian beliefs.
And quite a few quotes show her fury and anger in battle. This is just a side effect of having to have plenty of fighting lines in a game all about fighting. I'm sure she is only like this in battle, which is an appropriate place to channel your fury and effort. Many of her most threatening lines are not shouted or yelled at all: she warns the "Southerners" in a very calm manner not to mess with the might of the Freljord.
I'm sorry you aren't enjoying the new VO. But I personally think its a great expansion of her character and perfectly reflects the way she is in her recent comic without losing what we liked about Ashe. This new VO is far more vibrant than the old one.