I self-host Jellyfin on an old HP ProDesk PC that came from an office selling unneeded equipment. It's connected to my consumer wifi router/switch switch via Ethernet, and I stream videos on my TV via the Jellyfin client on a Roku Stick (which itself is connected to my network via wifi). Jellyfin streams great on my setup.

I know that's not very helpful in improving performance in your specific situation, but I just wanted to add my anecdata that Jellyfin doesn't require beefy hardware or above-average networking to run well. Sorry that I don't have much insight as to what was causing the performance issues in your setup.