KXIP are low on proper Indian players and they traded a premier Indian player.
Delhi Capitals already has plenty of spinners - Axar, Tewatia, Mishra, Lammichanne - they've added one more premier spinner now. Only dilutes all their opportunities too.
Would have made sense if KXIP picked a high class Indian player in return
No point trying to find a foreign player to replace and Indian player because of the 4 foreign players only restriction. Notice what is common between the teams which win IPL the most and are most consistent - Strong Indian players