I'm surprised how smooth the curve is, the author never has streaks where he loses a few hundred rating points. In fact I'm struggling to see he ever dips more than 50.

I've been on a similar journey over the past year, where I'm now around 1500 rapid on chess.com but in that time I've had streaks where I've been down 250 rating from my peak.

I don't know if I tilt super hard or if the author is remarkably resilient to tilt. It might also be a difference in how the different sites do match-making or adjust ratings and k-values.

I'd echo the benefit in learning some basic opening theory. It's not worth rote learning theory but it is worth having a consistent approach to games so you learn from the same patterns and can avoid opening traps.

If you play the same opening moves then over time you build up a memory of moves that you like in those positions and which will get deeper as you get more experience.