You see...I'm not!
I like Loewe but it can't be an alternative to Celine. Nothing can replace Celine. It's like Balenciaga by Nicolas Ghesquiere...Once over, it's done.
But Loewe has a playfulness that i love (and that is similar to Celine) even if JWA is a little bit limited as a designer. He is much more into decoration when Phoebe was really about the cut.
Phoebe's clothes resolved a lot of problems. They were sophisticated but not precious. Someone could have worn Celine from HtoT without looking like a walking ad while still maintaining a sense of personal style...A bit like Balenciaga back in the days.
Those clothes were designed with an active woman in mind...Unlike Victoria's which are designed with the idea of Victoria as that active woman...
As an alternative to Celine, really...The most honest answer that i have is Acne Studios. it's playful, not precious, fairly priced and well designed.