That might be a good idea on JBJ. Looks like $11 million for 2022. Defense was still very good last year and one wonders if the offense will bounce back to something in the 650 OPS range. That becomes a 1-2 WAR player who now has negative trade value (in other words he comes for free to get a Hader trade done).
Kiermaier is owed $14.6 million and is a bit older. He is coming off a better but still very average year. I'd say the odds are 60-40 that Kiermaier is better next year but he would cost a prospect or two.
Frankly there is a case to add JBJ for free (or such a minor prospect nobody cares) independent of any Hader deal. 50-50 chance of solving CF for a year at a cost only of money. And if it does not work maybe internal solutions like Moniak or Haseley or Vierling or Muzziotti are looking better by midseason (recognizing we probably deal at least one of those in the offseason).