Well the thing about mobility exercises is that you can "outgrow" them so to speak. It sounds like you have sufficient enough ankle mobility now that this particular exercise is no longer needed. You should reach a point where you get nothing out of a particular drill anymore. This is a good thing and means ankle mobility is no longer a pressing issue for you.
All that being said, for those with very limited ROM with ankle dorsiflexion it is an excellent exercise and the title of this thread is highly misleading to them. It'd be like me saying push ups suck because when I do a set of 10 I don't feel it anymore. Just like exercises, training volume, training intensity, etc...mobility movements are things you PROGRESS on...and yes, you are progressing.
So to say it doesn't work, and anyone who says it's the "best" are both ignorant, as its usefulness, as always, depends on the limitations of the individual.