Your interpretation matches my parsing of the changes to the rules, mind
you I had to read the paragraph about 15 times to make sense of the
numerous double or more negatives etc used to construct the sentences
and paragraph.

I called Uk Amex premium travel desk in the past week, initially the
response was, "we charge the highest amount". However taking the
person I was talking to through the paragraph fragment by fragment,
they agreed that it was very confusing. In fact they called on someone
else in the team to recount my fragment by fragment analysis of
the sentences and asked what they now thought. Again, confusion.

I suggested calling the OW help desk (assuming there was one).
When I got the return call from Amex, the resolution was that it
still meant we charge the higher amount.

What this says to me is that the paragraph is subject to frequent
misinterpretation, and that even OW help desk may come to a
different conclusion compared to those on this forum.

I would assume this rule has been inserted to comply to some
sort of EU (and Canadian) fair trading regulations. By wording
the paragraph in a manner that is indecipherable, is that
intention (or obligation) actually met?

Oneworld would do well to translate into english the paragraph
regarding point of purchase versus point of origination of travel.