they're not less intuitive than anything. #matrix clients are pretty okay, and every platform is covered afaik.

The biggest selling point on Matrix for me was the end-to-end encryption. It's what I used to convince my closest friends to switch. Fosscord is planned to have E2EE too and it's self-hostable, so it (almost) shares the main aspects of Matrix.
There do exist Discord bridges to use on Matrix, although last time I checked, they are far from usable.
Matrix is much more than a chat service. It can be used with IoT, for in-workplace chat (see the Element client's main goals). (1/2)

I don't think Fosscord will cover those two use-cases (mainly because of Discord's aggressive marketing towards gamers, so to use it for workplace chat is questionable).
Many open-source projects have their own Matrix room, so if you plan to contribute to some, I suggest you create one user on the many public Matrix servers.
Fosscord – because of backwards-compatibility with DC – in my opinion is a nice alternative to Discord and requires little effort – if any – from your friends to switch.

Your points are on spot, but some users would still choose familirity, ease of use (a discord client like thing) over privacy, and customizability (element, matrix).
And as you said: element is good for a workspace like environment, but if we want to create a community, then other clients, or other services are a better fit to be used.

Yeah, you might be right. It might be better for building communities and due to the way E2EE works, having large but secure group chats (about 500+ users) is very resource-intensive. Still, having the Fosscord instance be hosted by ELTE instead of big tech companies *khm* Microsoft and DC *khm* would be more private than what we currently have.
In my opinion, Element has a pretty understandable interface but each their own. All that matters is the promotion of FOSS projects over at our faculty.

running a #matrix server as of now (using the python-written server) requires resources indeed, but #E2EE doesn't, really [largst public test room has 250+ people and works well]. Especially if you won't subscribe to large federated rooms.
But running a "normal" server (like matrix.grin.hu) is manageable as well. And using matrix as a messaging layer is pretty simple, may be done with 3 lines of bash and curl.