They're different and have relative strengths and weaknesses. Despite being a contributor to piefed, I moderate a handful of communities on a lemmy instance and don't really have intentions of moving them. Overall, piefed is a lot less "mature" than lemmy, which makes sense because it is a lot newer of a project. It is getting better now about being more stable, but there are plenty of things that are still changing quite rapidly, especially on the api front.
As for python/pip/typing, I just don't see this as the major issue that some people seem to think it is. We aren't adding dependencies willy-nilly and the framework in which we are working (flask) is a very mature one that has stood the test of time. The fact that python is used for the project has tremendously helped the project in that it has allowed for a large number of contributions from many different people. Frankly, if piefed wasn't in python, it would not be nearly as feature complete as it is now thanks to the wide range of contributions we have received from folks.
This and || inline spoilers || were some of my early contributions to Piefed because I was so frustrated that they weren't in lemmy.