SmartmanApps

You would've done dividing by fractions in high school, which requires both. Fractions and division aren't the same thing.

But stating the division as a fraction completely changes my mind now about how this calculation works

But division and fraction aren't the same thing - the former separates terms, the latter is a single term.

(140-age)(kg) / 72(SCr) vs (140-age) X kg ➗72 X SCr

The different answers for these two isn't because of / vs ➗, but because in the second one you have added extra multiplications in, thus breaking up some of the terms, and SCr has consequently been flipped from being in the denominator to being in the numerator. i.e. AK/72Scr vs. AK/72xSCr.

academic arguments

The "academic arguments" can be ignored since this is actually high school Maths - it's taught in Year 7-8.

Especially when said person keeps making incorrect statements about Maths and ignores completely what is taught in high school.

Unfortunately, demonstrably, a lot of people don't know what to do.

The blog post claims it is popular in academy

The blog post also completely ignores what is actually taught in high school - as found in Year 7-8 Maths textbooks - which indicates how much credibility you should attach to the blog post - none.

I read the equation and was shocked that anyone would get an answer other than 9

As a Maths teacher, I'm shocked whenever anyone ever gets an answer other than 1. I'm not sure how you came up with 9 when you previously said you've only ever seen strong juxtaposition? You can only get 9 with so-called "weak juxtaposition" (which is wrong).

I’d actually say that the weak juxtaposition is just the simple one schools use

Schools don't teach "weak juxtaposition" - they teach the actual rules of Maths! As per what's in Maths textbooks. It's adults who've forgotten the rules who make up the "weak juxtaposition" rule. See Lennes.

We do teach children how to solve this. It's not children who get it wrong - it's adults that get it wrong! Cos they've forgotten the rules of Maths (in this case The Distributive Law and Terms).

WA interprets both symbols as having equivalent meaning

The wrong meaning. It interprets them both as a fraction bar, thus giving the wrong answer.

Division doesn't mean fraction. Division is 2 terms, a fraction is 1 term. Terms are separated by operators and joined by grouping symbols. If you change the division to a fraction you change the number of terms and change the answer (and you also would've just done division before brackets, which violates the order of operations rules).

And WolframAlpha did division before brackets (turned 6/2 into a fraction, thus making it a single term instead of separate terms, all before doing brackets), thus violating the order of operations rules.