"Input into the creative process" is surely broader than simply "painted the portrait". Artists most certainly never consented to have their works used as training data. To this extent, they might be justifiably pissed off.
Artists and designers have furthered their careers (and gained notoriety) by 'ripping off' others since the dawn of time. This used to require technical artistic ability; now less so. The barrier to entry is.... not necessarily lower now, but different.
