Hey Chris,
The MP2141N was derived from the MP1605, but can be configured to have a fixed output voltage and PG pin.
Yes, I believe the MP2141 has a better continuous power dissipation due to its improved thermal resistance in the EVB
Junction to Case temperature depends on the junction and the case, since the EVB provides a better junction temp, the junction to case spec is better. For more info on thermal rating, we recommend looking at our article : Understanding Datasheet Thermal Parameters and IC Junction Temperatures | Article | MPS (monolithicpower.com)
There is also a webinar in our youtube channel: Webinar: Understanding Datasheet Thermal Parameters and IC Junction Temperatures - YouTube
Hope this is helpful!
Regards,
Jonathan