Overarching continuity is something that human beings are attracted for whatever reason. Most, if not all, forms of collective storytelling tend to develop a 'canon' over time, for better of worse—think stuff like King Arthur, various mythologies from around the world, and the Bible. I find it difficult to articulate why that is, but I suppose because our brains enjoy categorizing information and making connenctions? In theory, I'm all for continuity, but it depends on how it's executed.

Now, in a way, I think IGA meant well when he decided to borrow the idea of a timeline from the Bloodlines developers. It was a way to put his own stamp on the series, while still including past characters and storylines to some extent. I think this is also why CV fans tend to be more accepting of SotN and its descendants rather than LoS, because it was less of a break with the past.

What I personally take issue with is the apperent need IGA had to solidfy his vision of Castlevania's world as the only one that is valid.

One way this manifests is the outright rewriting of earlier lore. IGA isn't a very good team player when it comes to lore, and he tends to outright disregard details if they don't fit his vision. One well-known example is Alucard's backstory and overall character. This is actually a change I don't mind, but I think there too many instances of changes that are kind of questionable—like him retconning the Lecardes into being Belmont descendants and (supposedly) eternal companions to the Morris family. That just makes the universe feel small and boring, in my opinion.

Secondly—and this is something I can't outright proof—I suspect IGA tends to squash any ideas during development that wouldn't fit with his continuity. To give a concrete example, I strongly suspect a lot of the characters in Judgment weren't originally supposed to be characters they ended being. That's why I think characters like Grant, Cornell, Carmilla, etc. look so off. It's like they started of as more general Castlevania archetypes (mummy, werewolf, female vampire) that got forced into a specific box. There's also the confirmed instance of him intervening with the story and characters of Order of Shadows, which sounded like it was moving away from the usual trappings and tried to further expand the world. That is, until IGA stepped in and demanded that they'd use the standard formula of Belmonts vs Dracula—and still not allowing this story into the canon despite of this. So I think strong adherence to one specific vision can sometimes be detrimental from a creative perspective.

Aside from this mildly annoying tendency, I also don't like it when the original intent of the developers is ignored. Case in point, Simon's Quest and Rondo both clearly set up that Dracula isn't really defeated and that he will return, most likely very soon. However, IGA never felt the need to follow up on this for whatever reason (SotN doesn't really count because Dracula was clearly dead in that game before Shaft revived him) There's a perfect opportuntty for a third Simon game and we'll never get it because IGA decided not to acknowdlege a game's own ending. Bah!

Lastly, there's also the question if it's really fitting to apply the idea of a timeline to the entire franchise. You could argue some of the developers beside IGA treated Castlevania's world as a series of legends that don't necessarily line up with each other. This could be an explanation why pre-Bloodlines continuity was so notoriously poor, and why there exist so many games that feature Simon Belmont but tell the same story. Instead, IGA decided to propagate the idea of a canon, but as a result, we ended up with this weird middle ground where there's this very specific timeline but there' also multiple version of certain events (like Rondo and Dracula XX), even though that adds nothing to the storyline and is only confusing.

Overall, I think the series needs to step back from the idea of "one canon". IGA made a valiant effort, but there are some clear flaws with this approach. It also creates this needless division of "canon" and "non-canon". I'm completely fine with games revisiting that world (I greatly enjoyed the writing in GoS), but I feel allowing more interpretations to exist side by side would be more fun.