IMO it's like anything else in life. One should know the upside and downside before making a decision. While it seems you've done a great job researching and doing the things necessary for your mandarin others (like me) may not be willing to go that extra mile and add it to the already exhaustive list of tasks for maintaining a saltwater tank.
I think that's where most of the advise comes from. Knowing (or assuming) that the effort is just that ; exhaustive.
It's the first time I've seen anyone articulate what they go through to keep one of these fish in a small tank. I'm sure this post will be referred to many many times in the future. It's the last sentence that wraps it up for me.
"If we were to buy any pet, dog, cat, rabbit, bird etc.. We would expect to buy food for them constantly"
I do expect to buy food for them constantly. However, if I have 3 dogs I don't expect to have unique setups for each one. I expect economies of scale. When I buy that 3rd fish I don't expect to buy special food, do special chores, setup a new main/qt/sump for each new addition .. and not again with the 5th and the 6th (generally speaking). Doin the herb/carni , wet/dry , additive/no additive thing keeps me on my toes.
It's a great fish (along with the blenny). I look at it like the decision to have a child. All cute and cuddly but am I ready for the enormous responsibility it brings day after day after day. I opted out mostly due to the same advice I see on here that I got from others in the hobby. After reading your 'how to' personally I'm glad I did. I would never have kept up