It depends on a few factors. What does the target audience consume? Is it YouTube videos? Or are they scrolling Instagram or tik tok? If so, an average video wouldn't work as well.

Also depends on the video's intent (selling vs educating), the message (is it written with the audience's needs in mind), the length, what platform it's being consumed on (sales page vs YouTube channel), how engaging the person/people in the video is/are, and other things.

Yes, if the stars align, video is helpful in marketing.

No, if they don't.

(You could waste valuable resources crafting a video that is hardly watched and doesn't convert.)