@Balladalidila 
Respawn talks about all these stats and metrics all the time. Yet they are nowhere to be seen. They do not make this information public or share any detail behind the claims they make. This leads me to believe that the numbers they claim to base their choices on are fake. What do they have to hide? Why not publish all the stats they reference on their website in charts and graphs. Ubisoft does this with Rainbow 6 Seige. It is very informative and helps explain choices the devs make.
Also, the thing about certain legends not being viable in solos. The devs have said they balance the game on a gun first philosophy and want character abilities to not be game changing most of the time. Based off this statement, the legends shouldn't matter. Respawn doesn't care when one legend has a 40% pick rate for the games entire existence, or when legends have less than 5% pick rate for their entire existence. Certain legends aren't very useful in many situations. 
The only reason solos doesn't exist in Apex is because the devs don't want to put in the effort to make it a permanent mode. It would also pull a majority of players to solos showing less and less playing trios and duos, creating longer match times and even lower quality matches. The devs just don't want to put in any effort. They are making billions on microtransactions by doing nothing. So why change.