I would be fascinated to know more about how SK felt they were mistreated in *A and to have the other side's perspective as well.
My impression has always been that yes, UA and LH were trying to protect their markets and boxed SK out. But if I zoom out and were to rank the *A partners in tiers, it has always felt like UA, LH, SQ, NH and TG were considered in the first tier of *A and the others were in a second tier. And it always felt like in *A, SAS wanted first tier treatment for second-tier behaviour. I have said it before, but amongst the other airlines in *A, SK always felt like that person at the group dinner who orders lobster and champagne, and then is surprised to find that the rest of the party isn't willing to split the check and wants to pay for what they consume.
First-tier *A airlines aim to offer an elevated experience (do they always succeed? no, of course not). If I were one of the *A airlines executives, I also would have struggled to understand what SK could bring to the joint venture to deliver a consistent experience with what the others in the first tier were offering . SAS has no first class offering, no business offering in Europe (they decided to confuse the market with "Plus"), the TATL and TPAC business flight don't really stand out amongst other airline's business class offerings, no premium lounge (e.g. Polaris, LH FCL, Thai Royal Orchid, ANA FC, etc), and until recently, a stunning inability/unwillingness to really invest despite the endless iterations of "SAS Forward" that only focused on cutting not just down to the bone - but into the bone.
Maybe given all of that, *A airlines could only see their flaws and not their potential. Good for SK that AFKLM, VC firms, and the Danish government did.
But I agree with the sentiment that SK has now found an alliance that is a better fit for their financial position and allows them to tailor alliance benefits according to what they are willing/able to pay. And it makes sense for them to join the joint venture in Sky Team because it's all upside for all parties involved. LH could have swooped in to rescue SK a few times over the last 20 years. It would be interesting to understand directly from them why they chose not to.
Overall, I am still very "meh" about ST. There are pockets of goodness such as AF business long haul and La Premiére, AFKLM lounges, Delta One lounges, and mileage redemption offers from AFKLM within FB at what seem reasonable mileage prices and availability. I very much miss *A award flight availability.