Ignoring the possibility of you having changed your account's name to avoid folks noticing that you're self-uploading, and trusting your word at this current time;
If the image is exclusively from the artist's Discord server, then include the original image link as the source and note either in the artist's commentary or in the comments (preferably the latter) that the image is exclusively on their Discord (and if their Discord is public, include it in their artist entry, though if not, include the avenue through which you could get access (like, for instance, if it is something Patrons get access too, include a link to their Patreon (and if they already had art on there too, then include it in the artist entry - in fact, if you wanted to give them further exposure, you would've filled out their entry with all their relevant social media accounts through which interested users can find their art)).
While this would warrant the posts in question being labeled with bad_link, it would still significantly increase the chances for the approval of the art.
In regards to approvers, they do have the liberty to approve what they want, and while this does filter art that one would consider genuinely bad, good art can fall through the cracks - hence the Upload Feedback Thread. It is also somewhat undeniable that there is somewhat of a bias in terms of the content of the image for some approvers, but others don't have such biases, meaning that for the art that you uploaded, you found yourself in the unfortunate situation of being unable to be approved by those biased and those unbiased. Again, calmly and respectfully asking in the Upload Feedback Thread may have proven worthwhile, as it may have given your uploads a second chance, because as mentioned, good art can fall through the cracks.