Champ is not alone in carrying two 4 irons in his bag.

Would you carry two irons of the same number in your bag? 99 with many tenths of a percent would say no, but there are a tiny number of players who do. And they are not anonymous golfers who have lost their minds a little bit, no. They are no more or less professionals. They are professionals enrolled in the best golf circuit in the world, the PGA Tour.
This is the case, for example, of the winner of the last tournament of this circuit held in North America, Cameron Champ, a tremendous hitter coming from the Web.com Tour and who recorded in the four days of competition at the Sanderson Farms Championship an average of more than 300 meters with the driver. This 23 year old young man, who should be followed closely because he promises great feats, carries in his bag two different 4 irons, the i500 and the iBlade, from Ping. He has made this decision because with the first of them, of hollow construction, he reaches practically the same 252 meters as when he used the 3 iron of the same i500 series, a distance that was too close to the one he reached with his 3 wood G400. With the iBlade, of a more traditional solid construction, he reaches about 220 meters. In this way, he feels he gains versatility and has that range well covered without the need for a 3-iron.
Champ is not the first PGA Tour player to use two irons with the same number. During the 2013 American Tour season, Keegan Bradley also carried two 4-irons (Cleveland CG7 and 588 MT) during his first round the AT&T Byron Nelson, and did very well: he signed 60 strokes.
Jon Rahm used a similar strategy this year at the US PGA Championship and also put two 4-irons in his bag, in this case Taylormade RSi TP UDI and P750.
Although the most curious case in this regard is that of Adam Scott, who this year has carried two 3-irons several times and has even done something much stranger: carry two putters in the bag.