EDIT: currently tumblr has borked the option to retrieve raw images so the methods below currently do not work. Will update when there is new info
All these pics are not their largest resolutions and have been downsized to the 1280 limit caused by tumblr. There is a trick that allows you to get their original filesizes and resolutions, which can exceed the default 1280 limit. To do this, you have to go back on the artist's tumblr and manually open each pic in a new window, then change certain words on the address as follows:
https://78.media.tumblr.com/80e12e25a9cf57d910869026f945d30b/tumblr_pbpc88AEXp1u97r0vo4_1280.png (1280x1067) into https://data.tumblr.com/80e12e25a9cf57d910869026f945d30b/tumblr_pbpc88AEXp1u97r0vo4_raw.png (3000x2500)
Note how "78.media" is changed to "data", and "1280" to "raw". If there is a security warning after changing the address, continue to proceed as it is safe to do so. Changing these parts will fetch the original file sizes and resolutions that these pics were originally supposed to be, as drawn and posted by the artist.