I really like this guy's content, but his way of speaking is somehow extremely hard for me to follow. Maybe it's because I'm not a native, but I really have to focus on listening, otherwise it's just a blur.
I'd disagree regarding such vids: these are more of a time fillers (how exactly is it useful to know the history of x11?). Hence, it's more convenient to listen to them as a podcast (e.g. via newpipe or mpv).
It's actually a good thing that visual learners get a chance to learn useful stuff by watching videos. Not everyone has the attention span required to read through a Wikipedia page.
It's his accent. He's British, but quite plainly spoken. There's quite a lot of "-ink" instead of "-ing" and "-ff-" instead of "-th-" (e. g. "nuffink" instead of "nothing"). The softer constanants are just characteristics of certain regions in the UK, but they can cause the sounds at the start/end of words to blur into each other.
To my ear, a fellow Brit, he's perfectly clear, but I can see how it could be slightly tricky for a non-native.
I don't disagree, but this video is absolutely worth the watch. I've read a fair bit on X history but there's a lot in here I didn't know specifics of or didn't know about at all.