I don't think there are any symbols that will do this for you easily, so you'll need to draw most of it. Thus you can just pick whatever style seems best to you for the look you're wanting to achieve.

As your initial drawing shows though, even a simple pit will give you a template from which to work with for this, although it may help to pick a spiked pit to assist in getting the descending pillar polygons to look right at their various angles. The wall lines alone help with those near the pit's edges, after which you simply need to adjust the angling as you work inwards. There's a spiked pit in the standard DD3 symbols, for instance. To make it rectangular, simply set different suitably-sized X and Y coordinates when you're adjusting the symbol's size. This will produce distortion (especially of the spikes), but as you're just using the symbol as a guide for drawing to, that shouldn't matter much.

The pillar polygons will need some shading applied to make it look like they're fading away into darkness (like the pit walls in your post here), which can probably be best achieved using additional polygons drawn over the "lower" parts of the pillars (try the darker Solid bitmap fills that have various transparencies built in), coupled with some edge fade effects to blend one to the next (you'll need to set up several extra sheets to get this to work well enough). It probably won't be quick or easy to do this, because you'll have to keep stopping and thinking about what to do next (I know I would, which is what I'm basing this on!).

If you get stuck, just ask again here. Or maybe someone else more technically adept will come up with a much more elegant, and swifter, solution in the interim!

Still reeling from the shock that the style wasn't called "Sinister Suers", naturally 😉!

If you're using the Outer Glow effect for the text, you might want to try just using Glow instead, as that sometimes seems to be less "misty" when used with text. Or you could try with a pale glow around some of the lettering, not a dark one. Larger text should help, certainly, but you may need to use different sheets for the different text sizes so you can adjust the effects more easily (and also perhaps separate sheets for the darker and lighter text colours).

Have you thought about leaving the hatching off entirely? You really only need it if there's nothing else to show what's solid and what's not, I suspect.

There's a possibility your system's showing "frames" (white lines connecting the nodes on a line or polygon). You can clear those from view using Ctrl + F, if memory serves (and if that's what was happening). It can be useful to show frames, as it makes picking out the nodes easier if you're trying to adjust them individually, but it quickly gets irritating when you're not doing that!

Nice-looking map, certainly!

If you're thinking of further tweaking beyond the point about the mountains (it's never easy deciding how much or how little you can cluster these things; it often depends on the style too, as some flow together better than others, and some styles won't overlap symbols properly), it might be worth adjusting the bitmap fill scaling for the woods and fields a little, to stop the repetition creeping in so much (most obvious in Evenwood), although that's quite a minor distraction once it catches your eye - so, sorry for mentioning it 😏😉...

I'd probably want to tweak the effect settings on the text too, especially the regional red labels that are fading into the terrain a little too much for my eye presently. Text tweaking is always one of the more difficult aspects of CC3+ mapping, as text is something the program doesn't handle as well as it might. It helps if you remember to set the fixed point before placing the text (albeit that gets a bit tedious if you need to change it every time), knowing the text may expand away from that point for different zoom and saved-image settings, or moving it about a little after placement, so that things like text on a curved line avoid having a letter over some key terrain element (always seems to happen for me...). I'd also be inclined to reduce the drop-shadow on the title text, and give that a somewhat broader outlining glow effect, just to help it stand out more than the "normal" text labels.

None of this is essential, or even all that significant, but you did invite comments!