So any of you reading this subscribed to Hollow of Dawn on Youtube may already know a lot of what I'm going to say so this post may be a lot of ground retreading. For everyone else, this is an exercise in accessibility from a story perspective.
The reason the Fate series and specifically Fate/Stay Night are so easy to talk about in terms of making a series more accessible is because they have a fairly good potential starting point for newcomers that doesn't exist at the moment. For those not in the know, Fate/Stay Night is a relatively old and now relatively popular visual novel that features 3 total storylines: Fate, which is a story detailing Shirou's quest to become a hero, Unlimited Blade Works, which is a story that delves into the psychology of Shirou Emiya as a character, and Heaven's Feel, which is a story all about answering questions about the previously established routes.
For most people who want to get into the Fate series the ideal starting storyline is Fate. The reason for this is because of the way the premise works and how the original 3 storylines were designed. Fate/Stay Night, at a basic level, is a story about Shirou Emiya and his goal of becoming a hero, using the Holy Grail War to achieve that goal by obtaining the holy grail and getting a wish granted.
Now, anyone who's read the visual novel will tell you that Unlimited Blade Works and Heaven's Feel are better written stories and while that is true for the most part, there's a caveat to that: Unlimited Blade Works requires you to already be acquainted with all the characters from Fate before you start and Heaven's Feel requires context from Fate and Unlimited Blade Works to function. Because of that, while Fate is widely considered the weakest of the 3 storylines, it is also simultaneously the most standalone of the three.
One might consider that, if you want to get into the Fate series, you just start with the Fate/Stay Night visual novel and go through it organically. A sound plan in theory but the problem is that the visual novel is quite heavy on text. Just for perspective, Fate/Stay Night has been stated to contain more text than all 3 Lord of the Rings books combined, quite fitting if you think about it.
That said, the amount of reading anyone would have to do especially toward the beginning just to start Fate is overwhelming for many. A better solution would be to have an anime to start with instead, since anime are easy to process and get through than a visual novel would be. The issue is that, of the Fate anime currently in existence, none of them adequately cover the Fate route. Fate/Stay Night (2006), also called Dean/Stay Night after the animation studio, is mostly Fate but mixes in elements of Unlimited Blade Works and concepts found in Heaven's Feel, not really anything in Heaven's Feel specifically.
Fate as a storyline is also the shortest of the three and considering Unlimited Blade Works barely works as a 25 episode series, Fate may have been lacking in that regard so filler was added. Then there's the Unlimited Blade Works movie by Studio Dean as well, which has a lot of the problems of Dean/Stay Night but also has the opposite problem of having too much content to fit into its runtime.
The next two options are also somewhat related to each other: Fate/Zero, the prequel to Fate/Stay Night, and Ufotable's Unlimited Blade Works series. Now, me personally, I got into the series proper because of Fate/Zero so I can't really say I should deter anyone who wants to use it as their starting point but one thing to note about Fate/Zero is that the story casually reveals things to you that were minor plot twists in certain stories of Fate/Stay Night. And, because I'm a "short for Richard" I'm going to reveal some of that stuff to you. For example:
- Within the first episode of Fate/Zero we learn that Sakura Matou and Rin Tohsaka are blood siblings, which was a plot twist in Heaven's Feel.
- Kiritsugu's gray morality as a chaotic neutral character was a plot twist in Fate. Prior to that, it was assumed that he was a purely heroic character.
- Also early in the series we find out that the Saber class servant used both by Kiritsugu and Shirou in their respective installments is a gender-bent King Arthur, which is two spoilers for the price of one.
- The nature of the Holy Grail is revealed at the end of Fate/Zero, which was a plot twist for Unlimited Blade Works.
- Fate/Zero also reveals to us that Gilgamesh, the Archer class servant for the series, never actually leaves the world, which implies his presence in all three storylines in Fate/Stay Night.
- Kirei Kotomine is revealed to be a sadistic psychopath, which was the final plot twist of Heaven's Feel.
- And though never explicitly shown, Fate/Zero shows Avalon's healing properties with Irisviel which ties into Shirou's healing ability in Fate and UBW.
Since many of these twists are just casually revealed during Fate/Zero's runtime, it gives the distinct impression that Fate/Zero was designed with the assumption that you've already read through the entire visual novel. Thankfully, Fate/Zero is high quality in spite of this but it does show how that can be an issue.
Finally, the Unlimited Blade Works TV series and the Heaven's Feel movie series both by Ufotable are not good starting points for largely the same reason: they both require context from Fate.
For any other series, this wouldn't be all that much of an issue. Most games or visual novels with multiple stories tend to have one canon way that they turn out and every other ending is simply non-canon, like with Higurashi: When they Cry and most regular games. The problem with finding the canon story of Fate/Stay Night isn't just that two of the three stories require context, it's also the fact that later stories go forward without invalidating any of the existing stories. In particular, the sequel to Fate/Stay Night was a visual novel called Fate/Hollow Ataraxia and while I have been told it's canon, the issue is that that visual novel is an attempted recreation of events from Fate/Stay Night using the limited knowledge of Angra Mainyu, which means it gives a sequel and follow-up to the events of the prior stories without confirming which one actually happened.
This is the Silent Hill 2 problem: none of the endings or storylines are any more valid than the others so any of them are equally likely to be canon. This means that for a full understanding of the Fate series you have to have some baseline knowledge of all three stories before moving forward.
Other stories, like Fate/Extra, Fate/Grand Order, Fate/Strange Fake, and Fate/Apocrypha also have nothing to do with Fate/Stay Night apart from character appearances, so they don't confirm what's canon either.
This is an issue that's unique to Fate. While plenty of games have multiple endings, generally, the branching paths are restricted to those endings and don't have too much branching outside the main story. Some games also have multiple story paths and even storylines, like The Witcher, Drakengard, NieR, pretty much any Yoko Taro game, either those stories have nothing to do with later games, like some of Drakengard's story paths, or the multiple stories are all the same story from different perspectives or with new information, like NieR and NieR: Automata. However, it's tough to say any story from Fate/Stay Night is any more valid than the others.
This means that all of them are required reading for anyone getting into the Fate series, not just the primary canon one. So this means that Fate is probably the best entry point ideally but, since that's not feasible for anime-only audiences, the best choice is probably Fate/Zero. Sure, it spoils stuff but it's also got the strongest hook of any of the series standalone.
That's all for now. Have a wonderful day.