This is not true. The "foot sweep" is considered as one of the 10 best signiture moves used in UFC. It's rated #5. If you are good at it, you can turn a stand up fight into a ground game quickly.
#10 - Flying Guard Pull
#9 - Slam
#8 - Leg Locks
#7 - Hammer Fists
#6 - Looping Overhand Right
#5 - Foot Sweeps
#4 - Thai Clinch
#3 - Head Kicks
#2 - Armbar
#1 - Liver Shot
http://www.cagepotato.com/10-best-signature-moves-mma/
In your opinion, is there such thing as "internal foot sweep" vs. "external foot sweep"?