pdf files are not against this forum policy. In fact many people prefer to have stories / sequences of images (and sometimes even text) compiled into pdf files. these people will certainly be thankful if your share your pdf files.
Personally, I prefer text in epub format and images in whichever image format the original source was, to preserve its original quality and because it is more flexible than pdf.
Converting images into one pdf file does not alter their quality, but with image formats I can easily convert them in a more "efficient" image format at a small loss of quality if I need to save space, or I can achieve a similar 'practicality' as a pdf conversion by zipping them and turning them into .cbz files. And then if I want to add new images to the file, I just unzip it, add the images and zip it back.
As far as hurting or not the talent, the formats of files shared here matters little.
The heart of the matter is that their works are shared here for free, so the question comes down to:
if their work wasn't shared here, would some of the people who enjoy it here instead pay them for it? or did spreading their work here make people discover it, who are now paying them to encourage them to keep gong and/or thank then for the work?
is the ratio of: (thankful new discoverers converted to patrons/once clients who now download for free instead) positive?