He is being serious but probably didn't word it that well.
What he meant is that all, or at least most of the doubters of DCL, have given Tosun a lifeline, saying that he's working off scraps, has got nobody in support, is new to the league and the like. When the truth is the same applies to both players, possibly more so DCL as he has been played out of position for half his games.
In my opinion, it's unfair to judge any if our forward players based on this season. The set up of the team has been so negative even Ronaldo and Messi would have struggled to score goals. Apart from Bolasie I think all our forwards and attacking midfielders need another shot in a progressive and offensive system. I'd have Tosun as first choice with DCL and Niasse as back up, and in some games actually play 2 up top. In the meantime I'd be giving DCL individual coaching on his weak area's of finishing, positioning in the box and decision making. If we haven't seen any development by the end of next season then Brands has a decision to make. Even then he'll still only be 22.