When Sion was first reworked and had his lore changed, we were given a connection to someone who knew him when alive (Boram) who decided to bring him back to life. Now, whether Boram brought Sion back because he needed his closest ally returned, a good general, or a more practical reason, we're not sure and based on the current lore that doesn't matter. What did matter was that Boram didn't expect Sion to become the monster we all know and love. A being so uncontrollable that he decided to lock him away.
The point being, Sion's warmachine like form was a mistake (or an intentional mistake from the Black Rose) brought on by a desperate man to a being who trusted him dearly. Sion's tragedy was that the man who he was before has been shattered, brought back unwillingly and unable to realize just how much he's been twisted. He's become the monster that everyone imagined he was in life.
The problem is that other people's perceptions of other people aren't 100% accurate. We still know very little on who Sion was when he was alive. We know his actions (though his "throwing the cowardly person in charge" section in his knew lore reads too much like old Darius to me) and we know his accomplishments, but that doesn't really mean much to invest in his character imo. Without some semblance of the person he was when alive, some reason to be sympathetic to the man looking in a fractured mirror, there is no tragedy behind him. He's just a dude that did a thing and became a weapon because of the thing.
Idk how many other Sion mains are like me, and I know that we as players cannot get the lore we want. But I figured that the purpose of new bios is to give us new information to work with. And outside of "last of a warrior culture" and rearranging the timeline of events so that Boram wasn't a near-immortal tyrant (because that was the reason why Boram used to be around since J1), all the new Biography does is just readjust what we already know.
I wanted to know who Sion was in life. If he had people he cared about, or if there were people who cared about him. Yes, I'll admit I'm a bit too stuck to my own headcanons that Sion is an ancestor to Riven, but when you don't have a solid idea of what a character was like then headcanon becomes more prominent.
Now granted, we don't need to know a whole lot about a character to have them be tragic. The best example of this is Warwick's new lore. We don't really know concrete details of who Warwick really was or who really knew him before he turned. We have suggestions, with Singed's observations of him and Warwick's interactions with Jinx, but nothing that actually stats Warwick was 100% X. What we have an idea of is that Warwick was a horrible man that was trying to be a better person, only to have that door slammed in his face as Singed kidnapped and mutated him. Warwick is tragic because he's a monster who tried to be good, but has been forced to become a monster. Yet despite this transformation, he tries to focus on harming those worth it. It's kinda like Krieg from Borderlands 2.
The key thing here is that we know a desire from Warwick, and we see it ripped away. We don't know why he had this desire, but we have it. With Sion, his desire as we know was to defeat the Demacians that were pushing away Noxus. He accomplished this with his death, but then people brought him back. Based on this, his character shouldn't have a problem being undead and killing, but his in game lines, lines written with his intended lore at the time, paint him as being possibly sickened by what he's become for the short lucid moments he has.
Sion is a monster, but he is also a man. We know the monster, and we know the legend, but we don't know about the man behind it all. Who was he really? Did he love? Did people love him? Was he driving forward to J1 knowing he was leaving people he cared about behind, or was he truly just a Noxian patriot who cared only about how many flags they planted?
This is what I want to know, and this new biography doesn't answer this for me. Maybe it does for others and I can't see it. I can only hope that Riot treats Sion as a character in the future, rather than an obstacle to be overcome by someone else.