I'm fairly certain that for a good chunk of the show, Worf is technically the commander of the Defiant, not Sisko.
No, Sisko was the commanding officer of the Defiant
for the entirety of its time on the show, except for the brief period during the war in which he had been given duty on the starbase and Dax was placed in command. Worf was never commanding officer. This is evidenced by the fact that Sisko and Worf have more than one conversation about the potential of Worf becoming a starship captain one day, including one conversation in which Sisko says it is less likely to happen because of Worf's actions ("Change of Heart").
In fact, it's never entirely clear who the first officer of the Defiant is. In the third season, it is clearly Kira, and I believe stated as such on screen. However, once Worf joins the cast, it seems to be murky between him and Kira. Sometimes Worf acts as though he is, sometimes Kira acts as though she is. I also don't think they make it clear who is placed in command of the Defiant
at the end of the series when Kira assumes command of the station.
Perhaps you're right, but we did see Worf take the Defiant on missions without Sisko multiple times, so it's certainly not unreasonable for Worf to be in command of the ship during FC.