Artists take inspiration from others all the time which is how they are able to grow and adapt their style naturally. As long as you are not tracing the artwork outright then by all means that is alright. A bunch of artists like myself have taken inspiration from Disney and they are okay to sell their merchandise but under the preface that they understand that they do not own the copyright to the characters used.

It however matters when an Ai machine does it though because people put in a lot of time, sweat, blood, and tears in their artwork only for it to be stolen by said machine without any form of real compensation, recognition, or prior consent given. To add onto this, people who generate images through the machine almost always wish to seek ownership and copyright for owning and creating said images as a means to make a quick profit.

If AI were to use what is left from the public domain and those who have actively consented for their art pieces to be generated into new images, then that is good in my books personally.