Selfhosting

If you want to host your own genealogy tree all options were (are) fairly janky. Gramps.js is the best options in my opinion.

Why now?
They finished core features that let you manage the tree fully online.

Gramps started as a desktop java app... and that desktop app works but synchronizing it is mess. The Gramps.js repo started using same data structures just new UI and finally they added delete function finishing CRUD bigo.
This means you can use the web app without ever using desktop app and since it is all hosted everybody who cares can contribute ~~without~~ with less of a risk of corrupting all the data.

Cons.
I think gramps.js is still incredibly janky (you have multiple objects that are handled independently for a single record i.e. family and person) and the maintainers priorities are bazar (implementing delete 2 years after starting the project and adding UI niceties like maps and alternative graphing views...)

Importing.
If you have your genealogy on some site somewhat curated you should be able to export most of the core information and import into Gramps.js (pictures can be an issue). For the import you may need the desktop app to convert to correct format (desktop app still has a lot more features and if you need to do merges I recommend using it ).