While Towns wasn't the incorrect first overall pick in 2015, it was also a draft that didn't feature an all-time great.
The NBA Draft isn’t of the same quality every year. Look at the 2000 draft as an example of one that lacked any star power.
There are some drafts where there is a clear-cut top prospect that often pans out and has a wonderful career. Think Tim Duncan, LeBron James, and, through two seasons, Victor Wembanyama.