Installing Synapse with docker and a TLS reverse proxy is a relative breeze. Like almost all server software, it requires some setup and general LInux knowledge. I haven't personally noted a lot of performance issues, but I concur that choosing Python (they even started with version 2) was a bad design choice. Good for prototyping but definitely not suitable for large-scale production usage. Hopefully Dendrite will reach feature parity soon. Moreover, they're doing some serious work on the p2p end and a working client exists already (https://p2p.riot.im).

I don't think Element has a bad UI, but there's definitely some room for improvement. Am not a fan of their use of HTML/CSS/JavaScript, I would have preferred a Rust GTK/Qt client but I understand that at this point in the project stage it's important to support the widest variety of platforms to serve the largest possible userbase. Performance and optimisation can always come later.