question about niche relevancy

Can I make you a question about niche relevancy? If I have a website on the Arts/Music niche and I rebuild the website to hit the Arts/Comics niche... is it still niche related since they are all in the arts niche? Or they are different since the topic is different?
Also what about videogames? Why they couldn't be related to the arts niche but they own a niche by they own?

different niches. The site would have different competition in the serps and would rank differently. If you fundamentally change the target keywords in the content it is a whole different game.

There has to be some common sense as well as a degree of latitude.

People associate The Arts with paintings, classical music, poetry, literature. So mixing Dickens, Hardy, Shakespeare with Fantastic 4 is a little far fetched.

Videogames come under the headings technology or entertainment, you can't just shoehorn everything into 1 niche due to the 7 degrees of separation rule of thumb.