While I do understand that Echoes is a very divisive game and I can see why you'd come to this kind of conclusion on the game, I feel somehow obligated to talk about a lot of these things. (Note that I'm not particularly trying to convert you as much as give context for why a lot of people hold it in high esteem for the same reasons you dislike the game.) The environment for the dark world was supposed to inspire feelings of dread and claustrophobia. The dark world isn't a place you want to be in. Everything you are told in game whether directly or indirectly through logs and cut scenes during the early segment prepares you for the reality that, despite Aether's homecoming banner reading "Welcome to Aether, now get the fuck off our planet", you will have to traverse every nook and cranny of this planet and that included an area that would be toxic to simply exist in. For someone first playing the game, it's a real fight against your own nerves to enter Dark Aether properly, let alone persevere through it all. The thing about this is, it's probably one of the best realizations of a situation in gaming where you have to bite the bullet and come to grips with what is in front of you. Retro succeeded in creating a truly hostile and almost player hating environment. For someone like me, who went into the Metroid series with Echoes thinking it was equally about trekking through dense labyrinthine locales as it is traveling with a constant sense of "curated dread", Echoes was a masterpiece and its overall visual design does support my thoughts even now, 11 years after its release.
While I do agree that the overuse of dark purples and reds in Dark Aether's color palette was to the detriment of having potently and immediately iconic areas or visuals within that dimension (unless you're a nut like me), I feel as though the visual design of the architecture in the dark world was excellently executed for the mood and atmosphere they wanted to give the players. The contortion/degradation/defacing of things prominent in the Light Aether version of certain rooms, the constant use of segmented worm like bodies, squishy organic material, gigantic multi-schlera panels invoking eyes all about the world and parasitic creature husks for the Ing structures, and the warped skies giving way to massive dark lightning storms just created a vision of an Edritch high level abomination where you were thoroughly unsettled between the combination of stationary and moving sights. Aurally, the dark world's chopping and sampling of the light world's main themes with a deeper guttural bass imposed over them liberally preyed on your familiarity with the more tame Light Aether over world. The imposed thumps in these tracks emulated the familiarity of heart beats and acted as an aural reminder that there were un-quantifiable "things" going bump in the dark all about you. If that wasn't enough, the shrieks and cries of the dominant living race ringing about in the far distance of most areas of Dark Aether only served to intensify the feeling you have of wanting to come up for a breath of fresh air after being submerged in Dark Aether's murky density.
The biggest reason why I will defend Echoes to the death in its use of the dark world trope though is due to the immediate and dramatic feeling of player empowerment as you gain the power ups through the course of the game and start realizing you can take more risks, you can last much longer, you can hit things harder, and you can travel further faster. There is an exponential curve on how powerful and flexible Samus gets in this particular game and the Dark World acts as both a check on this power and a taunt to the player. "Do you think you can overcome your nerves and step out into this segment of the world as you are?" You see your armor melting off and amorphous crab-tick-flea things three times your size running about on fourth dimensional plains all about and the first reaction is "fuck no", but when you get that first taste of disintegrating these creatures with blasts of light/super missiles/other satisfying weaponry, or you realize that the life restoring safe zones are structured in a certain way/you can manage your health reserves better and you revise and optimize your runs through the dark world despite losing chunks of health which later become trivial loss which even later on becomes a zero net loss, or suddenly things which are visible to your eye but seemingly beyond your ability to interact with are now easily turned on their head or dispatched with molten death, the infinite cold of space, or annihilation, it just becomes a greater impetus to see just how far you can trudge through this hostility and master the elements. Trips from the Dark World become less necessary evils and genuine tests of how far you can push back the world that pushes down on you.
As a final note, the idea of a dark world isn't a bad thing despite its overuse in games, Nintendo or otherwise. It's all about the execution and for both the time period and the feeling it was meant to invoke (a suffocating tension that gradually gives way to a feeling of complete mastery of domain), Echoes is a master stroke example of the trope used correctly.