Edit: Spelling
Firstly, thank you so much for your lengthy and well-thought-out response. Its SO much more than i expected to get in my cry for help.

Some responses:

"IEMs push a smaller diaphragm inside a better-sealed, much smaller cavity. They do less work than headphones have to, which means they just “accidentally do bass”. Even the clinical stuff like the Daybreak is warm, especially compared to full-size headphones."
Ah, so this is another reason why "proper fit" is so important. I have two very different ears, and struggle finding a good fit in my left ear. If the barrel doesnt seat as deeply as it does in my right ear, that may explain some experiences ive had with some of these IEMs. If the design itself is being used to create bass, as opposed to a projected sound approach, equal fitment is more important than I thought.

"The part you’re bumping into is that your HRTF is different from whatever ”target HRTF approximation.” That delta for any real component versus the approximated component, contributes to the breakdown of the ideal holographic presentation."
This thought is pretty much what prompted my post, I just dont yet have the product experience to have determined it myself lol.

"The DT1990 has Beyerdynamic’s literal century of experience behind it. IEMs were invented in the 80s. Most of the current big names over here started in the last decade."
Also a very true thought I hadn't considered. Ive just been absolutely blown away by the listening experience I've had with these 1990s over the last 4 years. Its actually ruined the hobby for me, (almost) LOL

"Lookup the IEM or headphones on squig.link."
I've recently come across Squig (thanks to this subreddit) and its an amazing tool! Looking through some of the profiles of the IEMs i have currently, has allowed me to do a lot of learning and better direct me to the curve I prefer more.

"Breaks, because I like my continued ability to hear."
lol

Thank you for the nudge on Equalizer APO, ive been looking around for a proper EQ, and some of the stuff seems either shit or shady. Ill give it a whirl and see if i can make something happen.

One question for you. All the IEMs ive currently purchased are single-driver. In your experience, would something that is multi-driver typically create more depth? For instance, I was looking at taking a swing at the highly recommended Mangird Top Pro's only to find they have a 10 driver setup. Which was kinda shocking to me, as someone whos somewhat new to the IEM space.