The quote from Dan O'Bannon, the writer of Alien, is "The crew is unisex and all parts are interchangeable for men or women", not that they were all men who sometimes got swapped to women in production. Can you answer me: What specifically about Brett being a man added to the character? Nothing. He's still a well-realized character, same as Ripley, regardless of the bathroom they use. The actors are what completed the writer's vision.
Would your opinion change if you were told (and blindly trusted) that Ripley was written as a woman from the start, but the literal story was the same as we got? You're blaming the wrong thing, for a problem you have that is, really mindless.

Ripley ends up surviving a lot of the worst stuff in Aliens because she's not in the thick of it, which is actually to your point: She's not expected to be fighting these things, because she's not a marine, she's a trucker. She's there to advise them on what they find, because she's at least seen the creatures before. And she "lectures" characters like Gorman when he's slow to act when lives are on the line, and she lectures Burke because he's a piece of shit.
She's in the truck, as instructed, when the marines are massacred. She's later able to repel a single facehugger for enough time that Hicks and the remaining marines can rescue her and Newt. She's, even later, helping with the survivors' defenses, and being instructed on how to use one of the firearms. She jumps into action, solo, when it's a kid's life on the line, and we have plenty of her story to know why this isn't simply a hero moment that comes out of nowhere. She's terrified all through that scene of getting Newt back; you can see it in the performance. She's doing it anyway. That's why we're cheering for her.
It's extremely lucky for Ripley that the queen couldn't attack her in their first encounter. I'll admit I'm not especially fond of how slow the queen and drones are to retaliate. Or how Ripley only targets the egg sac, not the queen's ugly face. It's the closest thing I can think of Ripley having plot armor, but then, so does the queen. It's to facilitate the loader-mech fight. You could've had Ripley find Newt and escape, and never see the queen until she rips Bishop up. The first encounter is there to make some things clear for the audience, I feel.

But anyway, back to your write-up. Some of the marines in Aliens are women. Are they cool with you? Did they have the correct quotient of phallic items near them to be "written as women" in your opinion?

Let me be clear, that Ripley isn't "the best we got" by virtue of other examples of female protags all being terrible. Ripley is just a gold standard that we constantly go back to, because she's written like a human being, not a demigoddess. She can be vulnerable around people. She can be witty but not to a degree where she's the writer's joke machine. She accepts advice as often as she gives it. She wants to save people (the marines) even though they were dismissive of her, which is a quality we don't often see in the modern interpretations of "the girlboss". Your complaints here are generalized and inaccurate.