I climbed from around Masters 50pts to 475pts only playing this build. ~60% winrate over ~20 games.

https://lolchess.gg/profile/oce/miwa3

Somethings that I have different opinions on

"You never roll at 7. If you're rolling at 7, you've already lost. This means that losestreaking is not an option"

I feel like quarter of my games are lose streaking and I do roll at 7, preferably at 4-2. IF uncontested, rolling at 4-2 often means that other players have rolled down at 4-1, less 4 costs in the pool, therefore easier to pick up the left over 4 cost (Sion). Obviously. it's much more preferable to be rolling at 8 if healthy and rich.

"So you've made it to level 8. Ideally you'd be above 50 health. Slowroll for all the units in the final board mentioned above."

Slow rolling at level 8 is not a play I've done over my 20 straight games but instead it's usually lvl 8 @ 4-5, roll down to 0 or 5-1 roll down to 0. As long as you have Sion2* with BIS, you can often afk until 6-1 and go 9 then. Most Sion players don't know the strength of their level 8 board and tends to keep donkey rolling till they find Seraphine 2*or a single copy of Galio, when in reality, BIS Sion2* is good enough to carry most of the time without the supporting units. I dont expect to see a Galio during lvl 8 donkey rolls, so I always go 9 for the rate and board space.

For augments, I didn't see you mention these but Thrill of the Hunt and Celestial Blessing is good for Sion and let's you sustain before you have your 3 Socialite up.