I think it's pretty well documented that intentional reordering happens and still happens

Should not that cause legal action - duly and factually?

Only if it's illegal.

It's a scheme with the purpose of theft.

You cannot have law as a list of specific cases: it must be based on patterns - "All arbitrary appropriation is forbidden and sanctioned", then further made into distinct categories to substantiate and differentiate the amount of gravity. All theft is illegitimate.

When the transactions 'arrive' in the bank's system should be immaterial, as they should be timestamped at the moment the card is swiped, matching the date and time the printed receipt I am handed has.

Regardless, the bank's mission is to make money, and they can make a lot more of it by adversely reordering transactions in their favor, it is not at all a reach to assume that they do so, and in fact have done so and may well continue to.