Well the biggest difference is the China Airlines shell seating where seats dont recline. That alone is a dealbreaker to me. I flew Starlux Premium Economy in January (SFO>TPE>Clark, then BKK>TPE>SFO on return) and loved it, $1800 or so and will most likely do it again next year.

4k resolution screens were awesome
Free WIFI for Prem Economy as well
Group 2 boarding (EVA Air is group 5 which bothers me)
A350s brand new aircraft 2-3 years old

The $1000 price difference seems high, its usually $300 difference round trip