The ratings chart tells the story... You can see the ratings for DS9's launch episode being the highest among all the others. It had the benefit of airing when TNG was still at the height of it's popularity. People saw it, and weren't impressed with what they saw. A space station, religious mumbo jumbo, whiny alliens, no starships only shuttlecrafts. Yeah no wonder DS9 ratings took a dive after the pilot.
Problem with DS9 I feel is the first 3 seasons were boring. TNG kept it light and adventure of the week. Tune in for a new adventure. Not your fancy try back next week.
DS9 had a shaky start. The preachy, whiny, and unsympathetic Bajorans grated my nerves
Dax was a know it all Spock type who borderlined Mary Sue with all her talents and knowledge
Odo hadn't been developed yet
The constant trolling by the Cardassians got annoying really fast. Not like they didn't have a government to run or anything.
DS9 didn't feel like a space station. It felt like a space mall with Sisko as the GM.
Season 4-7 we saw a change for the better for DS9. Unfortunately it came at the expense of ripping out things established by TOS and TNG. Breaking Kirk's greatest achievement the Khitomer Accords from Star Trek VI, and undoing TNG's Redemption storyline and by changing Gowron's character and making the Klingon Civil war a long forgotten footnote. The Dominion War was toyed and teased by the show runners for the better part of season 3, 4, 5, and finally jumped off in season 6. The first 6 episodes of season 6 to be exact. The the stories go back to episode of the week for specific characters with a mad dash to end the Dominion War in the last 9 episodes of season 7.