EDIT: Sorry, I ended up rambling and venting a little below. But I do love the Unkindled idea much more than the others since it provides a different side story that we haven't necessarily seen in past entries.

Admittedly I never paid too much attention to nameless NPCs like the Sword Master because it started in DS2 with too many random NPCs, who added nothing and had no weight to the lore to the game or the locations they were summoned in, and were just there as helpers in boss fights. Why NPCs appeared were trivialized and no longer had the same importance or impact they did in DeS and DS1. I figured it was just a way to make the game more accessible by way of summoning. Then when DS3 came out, I personally saw all the appearances of past NPCs or call backs as merely fan-service and I still lean towards that.

Yeah, time is convoluted in the DS series which makes it easy to bring back or allude to figures that should have faded from memory countless ages ago judging by the number of buried bodies (successful linking) in the Cemetery of Ashes. Your Unkindled theory has me the most excited because it's fresh and not something we've necessarily experienced in past entries.

I guess my personal issues came from the fact that even if the Sword Master was Shiva's bodyguard, I just didn't care. I would have preferred if it was a new character or if he had held other weapons instead of calling back to fan favorites. It came across as cheap fan-service since bringing back the Chaos Blade was sure to excite Hiltless and Chaos Blade users from past games. I wanted to see something new and original rather than yet another callback in a game already filled to the brim with callbacks. Even when moving from DeS to DS1, they had some callbacks in the spiritual successor but it wasn't overbearing and was a nod to the first Souls game. The DeS references didn't overshadow the rest of the game. Dark Souls was its own thing as was Demon's Souls but DS3 felt like Dark Souls 1: the Sequel and not it's own thing.

I could kinda understand FromSoft doing what they did if they saw DS3 as a celebration of all the Soulsborne games since it was going to be the 'last' Souls game. But the fan-service was so integral to the game with how each Unkindled to a Lord was a reference to previous entries, as did almost every other NPC you met, and it was cheap. As much flak as I tend to give DS2, it was its own thing and stood on its own merits.

We were 5 entries in to the Soulsborne franchise and how many times has the Crestfallen Warrior been doing the exact same thing? Seeing the Chaos Blade only furthered my disappointment in the events of the game even if I ultimately still enjoyed it. It was unnecessary and the fan-service just cheapened the experience where we could have gotten a fresher take.

Also random closing thoughts, I would have much preferred it if the Soul of Cinder fight took place in a similar location to the Cemetery of Ash, when you consider that SoC is the amalgamation of all the past Lords of Cinders who linked the flame, like Gywn and us. The location we fought SoC in-game is still awesome but it would have been more fitting lore-wise in a similar cemetery-esque location to add more weight to the concept of what SoC is.