Its not that hard to remove and the more aggressive you are with it, the more you distract viewers.
I have actually resorted to using match moving techniques to embed my logos into the video, so it looks like they are part of the scene, then you can just map the logo/text onto a side of a building or truck etc and it looks like it was meant to be there, but if you need proof of ownership, its there.
Or choose frame X to display a hard to see watermark, so if you need to prove its yours, its there and it will show up in 'their' work.
By which time, you can crucify them if they start to get any positive PR from your work.
Nothing would scare me more than stealing a drone video from someone, slapping my logo over it and putting it online a month after its already been up elsewhere and watching all comments archived for the rest of time exposing me.
Someone who steals your videos are not going to get anywhere.