Colluding is probably too strong of a word - even in quotes. Swedavia, as a business, has every interest in letting SAS put it thumb on the scales based on which airlines most likely to make long-term investments in the airport. SAS will out-invest all of the seasonal carriers. And for better or worse, alliances have a good track record of convincing airports to allow them to group together. It just will simply not make sense long term to keep AF and KLM out at T2 where they can't easily take advantage of SAS services in T5. But I get why LH and friends don't want to leave T5 because T2 is absolutely awful. It radiates sadness into the surrounding area and the cosmos.

I do agree with you that wide-body aircraft probably means T5. But is there any reason they can't put LH regional flights (and any other non-Sky Team regional carriers who might be taking up slots at T5) into T4 since it's connected to T5? You'd still get all of the benefits of feeder activity, stay within the Schengen zone, and SAS gets a de facto Sky Team terminal (just like it had a de facto *A terminal until September of this year).

It's just hard to imagine the status quo being allowed to remain this way long-term.