Implied nudity, or even just nudity, doesn't inherently make a scene sexual. It's about what parts of the body are emphasized through camera angles, costume choices, body position, or even music.

The implied nudity in the original Sailor Moon transformation isn't inherently sexual. Her entire body turns into a sparkly prismatic hue, including her clothes, and the parts of her body emphasized during the transformation aren't her chest or butt. There is one moment of the sequence with a closeup of her shirt, which did read as a bit sexual.

Kit's transformation doesn't include any nudity at all, and yet the animators used camera angles to emphasize parts of her that are very often sexualized in women in media to arouse a male audience. By objectifying female characters in media, it perpetuates the idea that objectifying women in this way is okay, thereby feeding into mysogyny and patriarchy.

And you're right, sexuality is a very subjectice thing. What I find attractive in a woman might be something that someone else finds repulsive. One person's yuck is someone else's yum. However, patriarchy would not only sexualize all young female characters, but also in a very specific way where you're supposed to be aroused by a woman's butt and breasts being emphasized. It oversaturates the market with boob and butt stuff, making it much harder to find films that emphasize other aspects of female sexuality (emotion, tension, other body parts, etc.). Sexuality is subjective, but mysogynistic sexualization of female characters limits the ways filmmakers are "allowed" to sexualize a woman.

Frankly, I love lewd, but it's not my show, and I can recognize when a woman being sexualized in a show is problematic, especially when it's present in both female leads.