Not exactly. G+ was contemporary with / the spearhead for that initiative, but the desire to reify login was something Google was planning to do for awhile; they just used G+ as the focus project around which to pin the initiative. Nobody at Google was really thrilled with having three (four? five?) credential stacks, all with their own bespoke tooling, concept of what an "account" was, security stories, and administrative needs.

(... the one thing that came out of G+ that has stuck around is infrastructure improvements. A lot of the stuff the G+ team wrote to support Google+ behind-the-scenes is still used at Google for other projects now).

And yet it is ridiculous that I have to respond to a 2fa on my phone just to watch youtube on my laptop, every. time.

I have a paid yt account fine, but watching trivial videos is not in the same class with accessing my gmail, or managing my gmail, or even managing my own videos if I were a youtuber. I'm fine with being one identity (well no I'm not but pretend I am) but those are not all the same activity or class of activity.

Hm. I don't, and now I'm curious why. My login never asks me to 2FA on my regular devices.

I've had that problem on websites when I turned on the strictest privacy settings.

Maybe they are subtly discouraging you from using those settings.

This.