Thanks for reading and the kind words Miklós!
I see two questions here, 1) importance of soft skills as a senior, and 2) the definition of "senior", so I'll try to address both:
Absolutely. I believe that any senior engineer is supposed to collaborate with one or more colleagues, where some of them won't even have a technical background, so being able to effectively collaborate is crucial. I believe that soft skills (and their importance) have gotten enough coverage these past years, hence why I prefer to focus on more technical-like skills with actionable advice.
The definition of senior absolutely varies, there's no question about it. A senior at FAANG has significantly different expectations to live up to, and they are appropriately remunerated for it. In my post, I purposefully do not focus on the actual promotion or job title, but rather on the mindset shift that has to happen for someone to make the step up. This is on purpose – I strongly believe that the title/promotion will follow anyone that makes the step up with their actions.