There is a very big difference between
"it can be eyeballed," meaning you don't need to use precise tools to get a reasonably accurate reading, but it certainly helps
Vs
"it doesn't matter whether you eyeball it," meaning there's no benefit gained from using the precise tools and in fact you may get more benefit by NOT using the precise tools.
Because the latter is exactly the advice I have seen. Repeatedly. It's not, "oh you don't have to worry about using the formulae, it's all really intuitive." Instead, it takes the form, many times over, of "DON'T use the precision tools, they actually have a higher chance of being wrong than just going with your gut on how difficult an encounter is expected to be."