So much of what was created for the TOS Movies carried over into TNG, including ships, costuming, and sets. TMP and Phase II were also rough draft versions of TNG. So, for those reasons, I group the TOS Movies in with TNG+.
To bring it all the way up to recently, PIC Season 3 drew the most from the TOS Movies and TNG. So, I'm not the only one who views them as part of the same package.
If I remember right, TNG was intentionally set 80 years after "the time of Kirk and Spock" (I'm too lazy to look up the specific fictional calendar dates, but I remember that line being used in the promotional material). But if you walked on a US Navy ship in the 1940s, the uniforms, equipment, and tone of the culture would have elements of what you would see in the 2020s, but it would be different while also being familiar. I think from TOS to VOY, you can trace a similar through-line where it all feels connected in the same way.
And, admittedly, people can point to places where there's story discrepancies, there's character moments that don't exactly fit with everything else, and nitpicky shit where the phasers fire out of the photon torpedo tube, but
Star Trek from 1966 to 2005 is united in accepting that everything that happened in a TV show or movie happened the way it was shown. Yes, the Klingons look different, but DS9 and ENT acknowledge it while playing around with it. Neither the TOS movies or the Berman Era try to disown TOS or any of the things that came before them and say "well, actually..." this is how the Constitution Class Enterprise really looked because it's too goofy looking for a 1990s-2000s audience.
All of those works
build on what came before instead of trying to
reinterpret it.
That's where my canon problems with DSC and SNW comes in. There is absolutely NOTHING WRONG with an approach that reinterprets that era of
Star Trek if you have a good story to tell, good actors, and great artists doing amazing work. It's still
Star Trek. Where my issue comes in with canon is fundamentally this: If you openly admit in interviews that you want to reinterpret
Star Trek and that's what this is, where things are changed to explore certain story aspects using legacy elements then there's nothing wrong with saying it exist as its own thing. If we can agree that there's nothing wrong with being open to changes, then we should be able to agree that there's nothing wrong with acknowledging there are changes and it exists in a changed setting where things are different.
I'm not a 100% canon absolutist, instead I just want the same level of continuity that was established during the Berman era. One specific poster will love to rip me to shreds again for saying this, but effectively 98% of Star Trek from 1966-2005 fits together... you just need to head canon that the Great Barrier from TFF isn't really the center of the galaxy, and ignore a few seconds here and there of dialog, like the great distances from "That Which Survives". Whereas D&SNW manage to conflict with practically everything already established about the mid-23rd century.
Speaking only for me, when those conflicts occur in episodes, especially with the series that are designed to be prequels wedged between certain eras, it takes me out of the story. I'm like "hey, wait a minute, how does this fit with..." and if it was divorced from the other shows and existed as its own thing that wouldn't be there.
If they want to explore a new iteration of Klingon culture in DSC season 1, Spore Drive technology that's forgotten about and never pursued by any other species in the galaxy (not even the Borg), a more-xenomorph version of the Gorn that was in conflict with Starfleet before TOS, the emotional legacy of descendants of Khan (that Spock never mentions during "Space Seed"), or a more emotional version of Spock that has feelings for Nurse Chapel (that's never even hinted at in TOS), just own it. Because if you continue to argue "NO, NO, NO, it's still all the same and it's still a prequel to TOS," then that invites a comparison to TOS and how well all of these changes will fit with TOS and everything that comes after it.
I honestly laughed out loud when I saw him say TAS can't be canon because Spock's hometown looks different in it from how it looked in the TOS remaster.
When I was a teen, I remember the canonicity of TAS was debated and generally not accepted to be part of Trek canon. That changed after Paramount got the rights to TAS in the 2000s and declared it to be canon, and writers in the Berman Era made references to elements of it, but even still TAS has story aspects that are REALLY hard to reconcile with Trek's timeline.
For example, how exactly did humanity fight FOUR wars against the Kzinti (TAS: "The Slaver Weapon") in the 21st century before making first contact with the Vulcans?