Back then Sony owned a big stake, less than 30% and it did them no good. After Yoichi Wada became CEO, he did shit on Sony. He ported and developed less exclusives for Sony. Do you really think this will satisfy Sony?
What if another Yoichi Wada appears?
No it will be not stake, they will get the whole company. No more risks. And I doubt Sony would gift Square Enix with a new and bigger HQ for several billion dollars in the most expensive place in Tokyo, Shibuya. New Square Enix HQ is very, very close to Sony HQ. Sony wouldn’t do this much effort if they weren’t to acquire them. Forget this stake buying, it will not be of interest for Sony Group. Fromsoftware e.g. is another case. Sony got only shares because Kadokawa doesn’t want to sell the whole studio or Sony would have tried to get Fromsoftware in full.