"Mythical" is a poor choice of word.
There were four players that scored 20 L1 goals last year. At least two of them played for clubs that our supporters would expect Oxford to compete with financially. One of the others was Charlie Wyke, a player who would hardly be considered a supernatural phenomenon. That leaves Clarke-Harris, who scored 31 rather than the 20 we are apparently demanding.
It is absolutely reasonable to seek to identify, or want the club to seek to identify, a player that can score 20. Three of the top six last season had such a player. Us and Hull both had a player on 19, which suggests that succeeding without such a player is the exception, not the rule. And it is worth noting that Winnall hasn't hit 10 league goals since 2016/17.