No it's not...

For the last 3 years I've been riding at an average cadence of 90....

This year the number has crept up to 95-97 consistently...This is after 2700km of riding...Without a cadence sensor I wouldn't know this.

I still use my cadence sensor to adjust my gear selection on the flats.

Personally I like having it and it's just another tool to help me track how my progress is going.