See :
https://augustafreepress.com/5-most-hard-seo-niches/
Check with these , it shows you 5 most hard SEO niches with more details .
See :
https://diggitymarketing.com/difficult-affiliate-niches/
Check with these too , it shows you what does it take to rank in the most difficult affiliate SEO niches . And it covers you some contents with more details .
See :
https://moz.com/blog/the-25-absolute-most-difficult-keywords-to-rank-for-an-seo-nightmare
Check with these , it shows you The 25 Absolute Most Difficult Keywords To Rank For - An SEO Nightmare with more details .
When it comes to ranking, the short-tail keywords are harder to rank because they're more obvious. People have thought of ski or skiing as a key phrase and because individually they have a high search volume, people want to rank for those phrases as well.
For long-tail keywords, it's easier to rank for because there's less competition.
See :
https://digitalmarketinginstitute.c...ch-engine-optimization_types-of-keywords_k7sq
Check with these it shows you more details about types of keywords .
Hope this helps !