When you go to the Pantheon Youtube page, do you use the 'sort by' function at the top-right side of the videos list, to see the most recent first?
There are about 73 vids on their page, going back to 2015. 24 of them are from less than a year ago. That's an improvement over previous years.
Also, have you checked out this terrific post by GoofyWarriorGuy? It has links to every stream he knows about, which includes the various Twitch Streamers who were invited to test play the game and show it on their own channels. Those streams aren't on VR's Youtube page, but many ARE on Youtube.
https://seforums.pantheonmmo.com/content/forums/topic/9329/stream-links-all-in-one-post
I also agree though, we can never have enough game streams.
If you go to the front page of our website and click on "more news" you can see a list of streams and videos that have been made public: https://www.pantheonmmo.com/news/
Or search our YouTube channel: https://www.youtube.com/channel/UC4MbaiykerIrjKWRA6407tQ
Also, "how often" is a difficult question, as one thing that has been a constant is change ;^)
There has generally been more content more regularly as development has progressed, but then there have been periods where the devs are 'concentrating' on something and we get little for a while.
I believe it's public knowledge that PA sessions are becoming much more frequent. There was over a year between PA4 and PA5, but we've seen a couple of PA5 sessions over the past couple of months and we should see more Soon(TM).
As for streams, there have been regular (monthly) roundtable recordings (not really 'streams') and irregular developer 'streams' sometimes with a varying mix of gameplay, reveals and some live chat question answering.
I would suggest if you want to miss nothing you subscribe on Twitter to Bazgrim @BazgrimTV, Minus @PantheonPlus, Nathan Napalm @TheNathanNapalm, etc. There are others too (sorry for not listing everyone!) but they link each other so you'll soon get them all.
I pretty much only use Twitter to keep up with Pantheon news. Oh, and of course, there's @PantheonMMO!