Great shot. I find my pictures always look dull when posted here, this is compared to how they look in C1P on the same calibrated monitor, so I was curious that you're finding a similar issue.
If you're working in AdobeRGB, that is a wider gamut than standard sRGB. I don't know if it's still the case, but it used to be recommended to export images in the sRGB colour space for sharing on the web, this avoids issues with software that ignores the embedded colour profile.
I'm pretty sure the effect that I'm seeing is a perceived darkening caused by the light theme of the website. As a test, I displayed one of the images I posted earlier using the website's viewer with the C1P window pulled up alongside it on the same screen and took a screen grab...

With most of the light surround cut off, the two images look exactly the same to my eyes (in terms of exposure at least), so I'd say any loss of impact is probably perceptual. Even switching to the dark theme doesn't help much, as it's not that dark, the post background colour is still quite light because the text is black and the viewing tool still has quite a bright background surrounding it.
I think a proper dark theme would be helpful (light text on dark backgrounds) as the generally bright background on this site does make a lot of posted images look dark.