There are certainly good arguments on both sides AFA splitting forums into very narrow, specialized categories VS lumping several into a more general topic.
Yeah...topics on "Guitars and Basses" should never pop up in a Mixing/Mastering forum...but likewise, some guys think Guitars and Basses should not be lumped together any more than Mixing/Mastering is (just to use one example).
IMO...categories that have a certain amount of "natural overlap" don't always benefit from being splintered into their own forum because they are either too narrow and can't sustain enough traffic on their own, thus cluttering the board with yet one more forum to have to scan and consider how it relates to Home Recording...or it often confuses some people as to where they should actually ask their questions...especially if their questions ALSO overlap across 2-3 aspects of Home Recording.
However, some are strong enough to be true standalone categories and shouldn’t be lumped in with others.
For me…Recording/Mixing/Mastering is a start-to-finish process, so there ARE questions that overlap across all three. People sometimes discuss certain mastering issues, and the replies point back to something that should have been done during tracking…so yeah, there is overlap.
But then you have some very narrow focused forums that have their own categories…like DJ & Hip Hop Production…???...so how does that rate VS Mixing and Mastering having their forums….???
There are many ways to look at it…none with very clear answers.
For me…Mics and Rack gear should be part of the Recording process…but I guess if there are enough single questions about Mics…then maybe there should be a forum just for that, though very often, a question about Mics is DIRECTLY tied to how it will be used for Recording!!!

Lots of things to consider there……
I look at forums as I would bars...
...while something positive can be said for having very fine-line "theme bars"...it's also nice having more "general public" establishments that welcome a variety of people rather then everyone turning around and staring at you when you walk in with that
"you don't belong here" glare.

That way...you can mill around in the crowd and get all kinds of great interactions and information rather than hear nothing but the same topics/perspectives.
Ever been at a cocktail party with a room full of lawyers???
I guess for this BBS….it may be best to just look at the activity over a period of time and to also monitor the topics that come up on the individual forums…and then use that to decide which forums should be lumped, split, eliminated or even added as new forums.