I think back-to-back ticketing is common practice and although airlines may discourage it, I do not think it breaks any rules and you should not be penalised.

If you buy two tickets:-

1. AAA-BBB Monday week 1
BBB-AAA Friday week 2

2. BBB-AAA Friday week 1
AAA-BBB Monday week 2

This gives you two Monday to Friday trips and meets the Saturday night stay rule.

These are two separate tickets and if you took all four flights, I cannot see that you would be breaking any rules at all.

But it's also often the case that buying the two tickets for just one trip (eg first Monday to Friday) can be cheaper than buying a single ticket only. This also is common practice. And again there seems to be precious little that airlines can do about it. Apart from losing money due to the cheaper ticket price, if the customer does not cancel their unused flights
the airlines get stuck with more no-show problems.

Where more than one airline serves the AAA to BBB route then the two tickets could be bought on separate airlines and then there is zero that either airline could do.