Just saw Enola. tl;dr the feminism isn't completely brainless.
It does play the "adults are useless" YA trope with the brothers but doesn't leave them so. Mycroft is something of a villain as he wants to send Enola to a "finishing school for young ladies" which obviously Enola has less than zero interest in, all because he's convinced it's proper (and from my understanding of the original character I don't think this is completely out of character for him). Sherlock, meanwhile, is trying to find both Enola and their mother, but he's missing some crucial clues that Enola didn't share, and regarding the marquis again she doesn't share the clues she learns, hamstringing him rather substantially so he's at least one (often more than one) step behind for the entire film.
As for the whole feminism aspect of the story, remember that the film is set in a historical period where women (especially young and unmarried women) didn't have many rights and the women's suffrage movement was active, which definitely does make the whole "anti-feminists are villains" thing lose its teeth as they're dealing with issues that aren't really around anymore (seriously how long has it been since we've seen anyone debating women being allowed to vote?). Also, note that Enola is not thrilled at the idea of feminist *terrorism.* Yeah the film quite literally calls out how bad of an idea it is to use violence to pursue even laudable goals. Otherwise, it also points out that those who aren't disadvantaged tend not to care about change, which is admittedly true (yes there are problems that lean against specific minorities in the modern day but then again today's government is compelled to at least recognize their voices, even if it tries to resist change).
As for Enola herself, she is not a Mary Sue. For starters, there's a fight sequence starting ~50ish mins in that's refreshingly realistic for a "pro-feminist" movie: a larger guy surprises Enola and overpowers her, she has to use trickery to escape the initial grapple, and even with her martial arts she barely escapes via plot convenience (in this case, it's literally explosive chemistry that just happens to be on hand in an area the fight enters). She also makes rookie mistakes, from trusting someone who is untrustworthy to getting herself put into lockdown at the school before she can make a proper escape attempt to not even considering looking for backup before confronting the BBEG, which while painful to watch are quite believable.
Also, I'm torn on how to react, but I couldn't help but notice that Enola never seemed to even consider that if she eloped with the Marquis, Mycroft would have no more legal power over her (which in the absence of her mother, she'd have to be aware that she'd be either hiding from the law or submitting to his rule with no other option _except marriage_ because of the laws of the time, at least for a few years), and Tewkesbury's enemies would suddenly have a massive incentive to let him live and vote as he wished due to the fame of his new brother-in-law, Sherlock Holmes. Admittedly maybe not a perfect solution for them both but I can't help but think it would have been a nice way to resolve both of their problems including UST lol, and part of me expects there to be fanfics where that happens.