Do you think bringing Worf to DS9 or creating Seven of Nine were creative decisions? They were decisions made to try and broaden the popularity of shows that were in decline ratings wise. Much like the Dominion War and the Xindi arc.
Worf, Seven, Xindi: yes
Dominion War: no
The Dominion was established very slowly and subtly as an adversary. It took like 3-4 seasons for the war to even start. It's not the same as the others which were immediate grabs.