I wasn't aware that William Barr made this claim prior to the testimony, so it's news to me?

William Barr has never made that claim. And he went on to say, right after that quote, that the Justice Department is conducting an investigation into this. That's very big news! Trump tweeting about how Obama spied on him is very different than the Justice Department dedicating resources to investigating the FBI, Obama, and Hillary Clinton.

Let's say for the sake of argument that it qualifies as news. Does it change the overall argument that "news" outlets try to claim far too much of our attention for topics they've already saturated, in the process failing to bring new events to our attention? Or are we just sealioning here?

I think it depends. If you use NYT or WaPo or WSJ as your primary news source I don't believe you'll see duplicates (if you only pick one of those 3, obviously each of those papers will publish their own version of the same story), excluding editorials. To a lesser extent this is true with the CNN news site, if you exclude their opinion pieces and "Analysis" articles (which tend to just link to their actual news article and add the potential political ramifications. Not true journalism, but not really an editorial either). Though the same can not be said of the actual CNN TV channel, which I find nearly unwatchable because they rehash essentially the same information over and over. I can't comment much about other sources.

As for failing to bring new events to our attention, I totally agree. The 4 outlets I mentioned above don't give enough attention to international news, stuff that really is important. Even in domains that are heavily covered bits get left behind. Like a Trump-appointed federal judge for the Federal Court of Appeals who had never been a judge of any kind before (The BAR recommends at least 12 years of judge experience for that position, the nominee didn't even have their law degree for 12 years) and was an active member of a SPLC-recognized hate group (who was confirmed by the Senate, btw). I don't have a single news article about that one, which is an absolute shame.

I'm just not entirely sure what stories should be cut. Maybe it will come down to just having a better aggregation system and UI to discover and keep track of these stories.