Well, it might be if you look at what is on TV, and do not count cultural relevance with influential.
TOS, and TNG are both much more cultural relevant. Almost everyone knows Kirk, Spock, and McCoy. And A LOT of people know Picard, Data, and so on.
However, when it comes to whats on TV, DS9 had a number of major factors that we forget.
1. Large cast
2. Diverse Cast (how many shows had the main star as a black man, a arab man as a lead role, and was aimed not at a ethnic audience at this time? )
3. None-episodic storytelling, which as been the rage of TV for the last 10-15 years.
Yes, Babylon 5 was doing some of the same stuff (Non-episodic storytelling mostly) and while i LOVE babylon 5, it a cult hit, and due to the budget limits, has not aged well. (And lets be honest, some of babylon 5 acting was uneven, while DS9 was able to afford a better set of actors on most shows.)
Also, the people involved in DS9 have gone on and done a lot of important shows. I would still say TOS is more influential overall, but modern TV has a lot more DS9 then any other Trek.