Why not? Dramatic retelling of the same in universe events. If you like, stage play vs. full film making. Or, as the TMP novel put it, TOS was a in-universe dramatization of Kirk's mission logs.
They are all equally canon, though some continuity might be looser. To me, it is "James R. Kirk" and "Vulcan/Vulcanian" levels of continuity, i.e. really doesn't impact how they can be in the same timeline. Mileage varies quite often.
Here's why I disagree. It's one to hand wave say the dialogue stating the massive distances covered in "That Which Survives", handwave the Galactic Barrier and the Great Barrier as both not literally being either at the very edge or very center of the galaxy, file James R Kirk under an in-joke between Kirk and Mitchell, and all the UESPA, Star Service stuff as Starfleet and the Federation as institutions were developed. Also, letting go of production errors like the deck count of the Enterprise-A in TFF, or rank pips. But it's something else to basically have the premise that the camera itself is consistently an unreliable narrator. To say ~ALL~ of TOS didn't reliably happen, especially when callbacks to TOS have been key plot points in other series. Where had you seen TOS, you could see what was coming. TNG, DS9, and ENT have all shown 2260s era Constitution class starships. So does that mean that the camera is an unreliable narrator there as well?
One of the points of canon / continuity is that even the bad episodes "count" and can have an impact later, like say "Datalore". That having seen "The Tholian Web" you'd go holy shit at the midpoint of "In a Mirror, Darky Pt I" as you knew what was happening before the characters. Or even with Picard season 2, knowing oh damn that's the Gary Seven transporter effect... let alone the Traveler / Aegis connection. Something can be paid off 30, 40 etc years later. So if NuTrek is saying, well you can't trust anything your eyes have seen before 2005, then and then picks and choses what counts and what doesn't on an arbitrary basis, it breaks that implied contract with the audience. If nothing really counts, nothing really matters.
Hence, why I think the best course of action is to just say ok STD / SNW are a reboot, essentially a do-over of the Abramsverse. What you all saw between 1966-2005 (TAS here or there) still happened, an still count. Which Lower Decks and Prodigy essentially have been doing, and Picard season 2 did. Ex Astra Scientia claims that Picard season 1, save for a glimpse of the Disco-prise, still holds up to the prior continuity as well. Let's assume Kurtzman has a partial stake in the Secret Hideout produced Star Trek shows. If/when his contract ends and Paramount goes with other people, they'll probably be constructively ambiguous about everything he did, lest they have to pay him royalties or a cut of future merchandising.
Based on the tweets made before that one, I don't think it was Terry who gave him access. Terry was surprised and even asked RMB was talking about, and RMB was very coy after that. They must have talked in private after that which lead to that tweet you quoted.
RMB does have insiders, he has known things about Discovery weeks before the episodes aired.
Oh yeah. Something really interesting must have happened at the end of STD season 3, that's for sure hahahaha...
RMB has mentioned several times he is friends with Bryan Fuller. Fuller apparently even gave him a Star Trek poster that was hanging in the Discovery writers room, advising him he might need to burn some sage(!) after accepting it. The general impression I get from watching his YouTube streams is he feels like Bryan Fuller was massively screwed over by Alex Kurtzman. He's also argued the basic premise for Picard was first pitched by Fuller as part of his anthology concept. This might be one reason he is so critical about NuTrek using concepts from Star Trek novels by DC Fontana and David Mack without credit, or cribbing from Ursula K Le Guin. Just imagine how you'd feel if someone got a nine-figure deal off the back of material from a friend, who was then left out in the cold?
Let's say Picard season 3 is in fact "good" in that it would appeal to a broader segment of the fanbase than the more limited cross section targeted by other NuTrek. That major course corrections happened. It'd be good to signal that to the people who've been greatly antagonized over the last five years. RMB would be a good guy to leak something to to change the opposition fan narrative. But, yeah, there are many black pills and YouTube grifters that wouldn't like to see Star Trek, Star Wars, Marvel etc course correct. So they complain about everything, even when things have noticeably improved. I'd argue RMB and RLM were reasonably fair with Picard season 2, while Nerdrotic and Doomcock were not.