Likely true. Taiji forms are usually one sided too, but then at one point you are expected to move in reverse.
I was Uke for a guy who practiced Aikido and Kenjutsu who only practiced Tanto dori against someone holding in their right hand. I hadn't trained that way, and stabbed holding with my left after my right wrist got torqued. During his test, with Sensei watching. Scratched him with the wooden knife, decided I wasn't a fan of that training. Sensei told him he should have trained harder.
Which is an interesting thing about training on one side - you only get one arm cranked on. And its the arm that makes a bigger movement when swinging a weapon.