Over the last 10-20 years this became probably the most famous misquote of any scientist EVER. This phrase was coined by social philosopher Herbert Spencer, NOT Darwin! Darwin’s view was rather “survival of the fit enough”, which leaves much more space for diversity.
Another common misunderstanding in this regard is to set evolutionary fitness equal with strength or ruthlessness. Sometimes it can mean that, but more often fitness is about adaptation to an environment or ecological niche. High levels of cooperation between individuals (social animals) or symbiosis between species often lead to excellent adaptation!