I don't think Ella was submissive if she did not like Serge as a person. Her cousin Willy was quite the master too, but lacked Serge's intellect and deep spirituality, both qualities attracted Ella. So she chose him.
As for Marie Paulovna, I viewed her story with a grain of salt. Most certainly Paul abandoned the children when she followed his mistress into exile. Why ? Because he gave her some of his dead wife's jewels to wear. I think if Serge care so much for Alexandra of Greece, he would be pained to see his brother ran off with :that woman". So Ella (who was also a close friend of Alexandra of Greece) never forgave Paul for ignoring his duty to his children. Her father Ludwig, never thought of remarrying until his children were all grown up. What a contrast ! I could sympathize with Ella's outrage. As for Marie Paulovna forced to marry against her wishes, new evidence debunked her claim. The letters she wrote to William of Sweden were mischievous and full of dissatisfaction with her aunt, but she was also happy to start a new life. Yes, she wanted freedom but also out of boredom. She like her father before her, also abandon her child after her divorce. Like father like daughter ?