Hm no.
Fiction doesn't sell better than non fiction.
Fiction:
+ easy to write (even a housewive can do it)
+ easy and cheap if you outsource the writing
+ niche/keyword analysis is not so much important
+ fast prduction (a good writer is able to write 5k words/day)
+ there is no right or wrong (a stroy is subjective)
- entertainment products are easy to outrank by competitors = no long term success
Non fiction:
- more expensive to outsource (because its a lot of research work or you need experts)
- slower production (because of the research)
- niche/keyword analysis has to be perfect!!!
- there is a right or wrong because it death with information
+ if you produce a really great non fiction book you can make big money for years because competitors can not reach your quality level and information never getting old = long term success.
Conclusion:
Fiction is the way to go when you start with less budget. You're getting fast results and you can build up a decent income step by step (it's just a numbers game). IF you have the stable income ..take your financial freedom and go to non fiction! Because there you can make the most money. You can sell non fiction books more expensive. People are buying paperbacks of NF as well (and they are willing to pay up to $20 for books). You can sell other products like video courses, mobile apps, physical products on your website etc. on your website. You can easily build a social network around your niche to make money with affiliate products and so on. There are thousands of possibilities that you'll never have with fiction. So non fiction is definitely the way to make the big money for years! My first book (non fiction) makes $50k+/year (only one book).
With fiction books I can increase my income by $1000-1500 per month. I have automated mostly every process of my fiction business. But guess what: I don't care about 1 or 2k more or less per month. I don't care if I make 20, 30, 40k per month because I was financial free and absolutely happy even when I reached 5k/month!!! So it's more important to save my freedom for the future because my fiction books (midlist products) will not run endless. But non fiction books can run endless.
So you can a) increase your income extremely by non fiction books b) save your financial freedom for years BUT it's more expensive and there's more risk to fail. That's why I would start with fiction.