Well I hope as much as Sage that one day someone will come and tell us some solution, but Im not holding my breath for it. All I know are ways to somewhat hide the issue, not getting rid of it entirely, and I tend to be reluctant to resort too much to them...
1. Having less steep elevations is the main thing I think. I am rather surprised it still shows up as much as it does in your flattened picture, but it is zoomed in extremely close and might not be as noticeable during gameplay. Obviously not saying flattening bunkers is a good idea... but having slightly less steep bunkerlips usually at least helps a little...
2. Using textures and alphas with more irregularity to them seems to help make it less obvious. Especially for the bunkerlip texture itself if using one (like the dirt or whatever in between sand and grass).
3. Using darker textures.
Your example has a very bright sand and the in-between texture is fairly sand-like, which I suspect might be the main reasons why it shows up so much (but there may still be some other reason). One thing I become curious about, is whether the same lines would show up if you delete the bunker and construct the bunker the same way from scratch except on flat ground initially and then "make" the elevations after the whole bunker is meshed out and seamblended... but it might still be the same...
When I made Nine Bridges was last time I experimented with it, I remember having the idea that perhaps the defects come into being during extrusion, and tested making two identical bunkers, one of them with extrusions and the other by hand with terrain painter, and the defects still showed up the same... so that didnt lead to any solution.
Sorry but its the best I can offer, I really understand how you feel but I hope you dont let it defeat you. Personally, at least thus far, I've felt like the issue can at least be kept mitigated enough to be acceptable, it doesnt need to look amazing when seen up close in order for people to still like the course. Just look at Augusta and Whistling Straits for example, they both have the issue to very noticeable extent if you go looking in the right places, but I think everyone still agree that they both are very, very beautiful courses
P.S. One option, if it suits the type of course you're making, can be to partly hide it with a subtle bit of planting.