Primal doesn't connect to relays to read from them, only to write to them, but I have noticed that it loses connection and won't post anything after a while, and I have to refresh the page.

For reading notes, Primal only connects to their own caching relay, which I have never noticed it having trouble staying connected to.

What a lot of users often perceive as Primal being really slow to load is when they are using custom DVM feeds, such as "Popular from Npubs You Follow." These feeds are not served by Primal at all. Instead, Primal requests a list of notes from the DVM, waits for the DVM to sent it over, and finally fetches them from their caching relay. The wait time from that DVM is often the slow part.

Videos can be a whole other issue unrelated to clients at all. Remember, this is a decentralized protocol, not a centralized platform. On platforms like Facebook or YouTube, they can ensure that optimization is done on the videos uploaded to ensure quick loading.

On Nostr, users can upload videos wherever they want. Directly through some clients that may or may not optimize the video for web, through a hosting service, or even self-hosted.

It's pretty easy to load videos quickly when you have control over ensuring they have been optimized and you only have to fetch them from your own servers. Nostr clients have neither of those luxuries.