Welllllll... here's the thing:
In every game before SwSh, the Legendaries already existed in the game and needed to be made more accessible so they weren't transfer-only.
Gen VI and VII doubled down on this and did literally all of them because they banned transferred Pokémon from competitive and needed all Pokémon to be possible to obtain natively, which meant every Pokémon you couldn't just breed to get a Kalos/Hoenn/Alola-born copy needed to be directly catchable.
Now that Dexit has been established, this obligation is gone; the only Legendaries they have a real
responsibility to make more accessible in-game are the ones that are already available through transfers. They used to need to make sure everyone had access to Latios because Latios was already in the game; they don't need to make sure everyone has access to Latios because Latios isn't in the game any more.
The list of Legendaries to cram into a feature like this is also way longer than it used to be:
- HGSS only had Gens I, II and part of III to deal with to finish what Platinum started; they ended up with 14 Legendaries.
- B2W2 only did Gens III to V, didn't have to include the past games' restricted Legendaries (there was no GS Cup format in Gen V so they wouldn't be in VGC either way), and even cut three of Gen V's own Legendaries after BW to make room; they ended up with 17 Legendaries.
- ORAS crammed in Gens II to V, and it already felt ridiculous... but let's count: 5 from Gen II, 8 from Gen III, 9 from Gen IV, 9 from Gen V; they ended up with 31 Legendaries.
- Post-DLC, SV are already going to have... 42 Legendaries (or 39 if we aren't supposed to count the Loyal Three - I dunno) and a further 18 Paradoxes, even if there are none left to be officially revealed (but I think everyone expects Entei and Terrakion, so 20?).
Even compared to SwSh, remember that while SwSh had every old Legendary and every Ultra Beast, SV also has 12 Legendaries and 20 Paradoxes that didn't exist until after SwSh! The list is not getting any smaller - if this is ever going to boil over and a line is ever going to be drawn, this kind of thing is going to be exactly why.
Then we consider the silly hypothetical that SV's DLC is to be anything like SwSh (all of the past Legendaries
and all of the Ultra Beasts, while already having all of the Paradoxes).
We'd end up with... uh... I might be miscounting a little, but something like 67 fully-evolved Legendaries, 10 fully-evolved Ultra Beasts and 18 Paradoxes? for 95 entire Pokémon (+4 more NFEs), many of which have forms, plus the three Galarian birds which are effectively entirely different Pokémon from the originals...
most of which are just there out of perceived obligation and to complete a set?
"All the Legendaries, every game" should
really be starting to look like a joke at this point.
The reason we should not count on this to keep happening just because past games did it is because it becomes actively
more ridiculous a commitment with each passing Gen... just like having the whole National dex in the first place, and they made the right choice there eventually!
I want next Gen to be more selective than these past two about how many Legendaries come back, personally...
HOME was a mistake, transfers were a mistake, hashtag #BringBackRegionalDex and all that--
Edit: oops, we posted at about the same time, but one more thing!
We knew about everything except Magearna, which seemed to be a last-minute addition to IoA as a HOME tie-in (it was the reward for completing the National dex but couldn't actually be brought over to any game until then).
That said, Shaymin has also been established as returning in the DLC this time around but wasn't datamined (while everything else has aligned perfectly with the datamines so far), so transfer-only Mythicals might still be in a state of flux!
I seem to remember Khu (the main reputable leaker) implying that the transfer-only Hoopa was a pretty late addition to base SV, too; maybe they just don't always put much thought into those until the end?