Those genres all mean something to me as I've invested a lot of time and effort in more obscure music - I'm someone who considers if I'm listening to brutal death metal or slam death metal for instance
Whilst there is certainly similarities between some of the genres you've named, there is also nuanced differences
Doom, stoner and sludge for instance will have elements of their sound that crosses over - in these cases they probably all love Black Sabbath - but there will be differences between a doom band and a sludge band and stoner one will be different still
dreampop and shoegaze are very close bedfellows and you wouldn't be wrong to say the same for mid-west emo and indie, however you can make a distinction between them if you want
You don't need to sub-divide genres at all if you don't want to, but then some folk will have vigerous debates about for example, what makes a band post-hardcore rather than emo
The purpose, as I see it of these categorisations and sub-genres is to aid communication when describing to others what a band sounds like, so I have an idea of what I'm going to hear and how to find similar sounding acts if I like it
However, there's no need to make the distinctions if you don't want or need to.
Apologies for what is probably a very autistic answer