You are right. According to the definition of social media, Lemmy is social media. However, "social media" would by definition fit any kind of digital communication media. A forum, or a blog, or an IRC channel are also, by definition, social media.
I would argue that the social media has a distinct association with Facebook, Instagram and the diverse spawns of those, and by association doesn't fit anything else. At best, we simply lack a different term, which splits "old-school" stuff like forums and blogs. I view lemmy more like a forum. You have categories, and users can go into categories to start discussions. You don't follow anyone. People also don't create and post their own content, but rather seek discussions or share other stuff from the internet. Your goal is not reach, follow count or like count.
It is social media, but it's definitely nothing like Facebook. We simply lack a better term.
Not monotonous but non-creative. Any machine can do non-crative work. No machine can do creative work. You don't need creativity to farm food, you do need creativity to invent new medicine.
In an average company that isn't scaled worldwide, usually the cost of labour is 40-50% (paying wages). This means if we replace humans with robots, doing repetitive and non-creative work, we can make stuff cheaper by a lot. OFC unless the company boss, who is then left alone with all the profits, just decides to keep the prices with no people he needs to pay anymore.