I was originally against keeping fish as I thought it cruel to contain a creature when in nature they have so much space. Then I spent a couple months scuba diving as part of reef conservation and watched fish (albeit marine) in their natural environment. And I realised that small fish don't know that they have so much space because they stay in a relatively small area. That was when I thought it might be nice to keep fish at home. So I looked to set up a micro environment. I originally wanted a south east Asian biotope, and chose plants and fish to suit. But I think that was perhaps a bit too ambitious for a newby fishkeeper, so I've gradually relaxed the boarders. Most of my fish and plants are Asian, but I've got the odd exception - Bertie my BN. But my aim is to still to create a micro environment where the fish and the plants balance each other for needs and clean up.
It took a while to find the balance, but I have since made major changes so I'm still in the process of working out what that new balance is. And it's not a static target, due to fish and plants growing, some of my fish are old aged so I am expecting deaths before I find my new sweet spot. I've not had any babies (in the tank!) yet, but that would also change the balance.
I used to think of 3 layers in the tank - top middle bottom. But since adding my fiveband barbs I've realised there is another layer, non benthic (free swimming) fish that live in the bottom third of the water column ie near the substrate but not on it. I've not yet worked out how that will affect the overall balance / aesthetic 'fullness' of the tank.
It's also worth remembering that we judge stock levels by fish length, but that isn't necessarily the best reflection of the effect a particular fish will have on the tank.
For example I have a BN Plec whose calculated size is 12cm. And kuhli loaches whose calculated size is 10cm. Their contribution to the balance in my tank is wildly different. Bertie is far more messy than his calculated stock size (even though he's an algae eater). A pair of BN Plecs is probably the most that my tank could sustain (24cm). But my kuhlis are long and thin and are more clean up crew than mess contributor. My tank could probably comfortably sustain about 15 if I didn't want any other benthic fish (150cm).
So there is a lot more to consider when finding the right stock for a particular tank than just the calculated stock %. (Which is why it is heavily emphasised that it is just a guide).
Ps
@Matt I didn't read your post as a rant at all! Didn't consider it might be until you mentioned it.