I've only ever heard the MEST in the sound demos that Dan's Audio Reviews publishes on his YouTube channel, as kilobuck IEMs are pretty firmly out of the realm of obtainability for me, but just from those sound demos I can concur that the MEST's perceived resolution and imaging capabilities are addictive. Really puts you "in the room" with the performer in a way I haven't heard from anything else. Regarding the perceived veil in the mids that you experience with the MEST in A/B testing against the Dusk, the MEST is known to have a lack of energy in the ear gain region of the frequency response (between like 2-5kHz) which affects the 'bite' and forwardness of vocals and certain instruments. It's an area of the frequency response the Dusk puts emphasis on, which is likely why you perceive the Dusk as sounding more open and forward.

No idea where you stand on EQ, but if you're open to it, 2 or 3 filters in a parametric EQ could get you a very similar tuning in the mids of the MEST as there is in the Dusk. This would change the overall tonal balance of the MEST from something of a unique U-shape to more of a bright-ish Harman target, though, and a change in the MEST's tonal balance could also possibly affect its unique imaging capabilities, but I have no way of confirming that, as I don't own the MEST.

Parameters for the EQ would be:

Filter 1: Peak Filter, 3kHz, 3.5dB, Q Factor of 1

Filter 2: Peak Filter, 3.8kHz, 2.5dB, Q Factor of 3

Filter 3: Peak Filter, 6kHz, -1dB, Q Factor of 1.41

There are a couple other small adjustments you could make to the MEST's lower mids and bass to get those regions closer to the Dusk's more lean tuning, but I don't think those areas are likely problematic in the MEST. I've heard the Diva is an excellent IEM from reviewers I trust, so I don't think you'd go wrong in buying it, but if you're down to try it out, give EQ a shot before going out and spending another kilobuck on the Diva.

For me it's just been BL-03 > ER2SE so far. There have been a few tws purchases here and there, but I consider those separate from my wired sets. Thinking of grabbing the S12 as my next (and possibly last) wired set. I don't feel comfortable spending more than $200 on IEMs, and from what I hear the S12 is competitive with stuff in the $500-700 range for detail, so I think I'd be cool with stopping there.

I only own two IEMs both being 1DDs in the ER2SE and the BL-03. Love em both, and they both see daily use from me, Blon for casual listening and bassy genres, and ER2 for critical listening and vocal-centric music. I sometimes think about buying the IE 600 or one of the big hitter all BA or tribrid sets, but then I remember I got the ER2SE for like $50, and I can't imagine anything out there sounding THAT much better than it for me to be shelling out over 10x what I paid for it.