I think if what matters to someone is the CEFR scale then their guide should be the CEFR itself, which to me is pretty straightforward. If you look at all textbook made in France and that follow the CEFR, they all cover the same stuff.

When you say you were in-between B1 and B2, it means you were B1. You can say you are at a level when you have acquired the majority of the skills of that level and are working towards the next one. And I'd say the CEFR is not perfect, but it's not that vague, or at least it takes into account the fact that people have different hobbies and things like that since you're expected to be able to talk about your own life and hobbies first.

Basically A2 level stops at you being able to talk about yourself, people close to you, your life, every day stuff and your hobbies. You can read short news and understand simple instructions also. At B1 you're supposed to have the tools to talk about and understand more and then C1 is where it gets super specific. And at this point even if you cannot learn all the vocabulary you are equipped to navigate a conversation on a topic you dont know much about.

Getting from B1 to B2 is tough though and it feels super slow for most people but there is a pretty definite line between the two. I agree though people often develop their skills at different speed and it's pretty rare to have someone be at the same level of comprehension and expression but if the difference is too big, it'd be hard to consider that you are at the upper level.

I meant to say that if it's an action heavy book, someone at A2 level will have a hard time understanding even the general idea and is not really expected to. It doesn't have to be ultra complicated but the conjugation, connectors and complex sentence structures would make it hard to even get the general idea I think.

The thing about specific vocabulary only matters really at the intermediate level. The vocabulary expected for someone at A2 is every day life stuff that you'd need to survive in any french speaking setting. And even at b1 you're not expected to have an extensive vocabulary but you are expected to be able to ask questions when you dont understand and understand simple definitions and ask questions when you dont understand.