You need a strong and versatile left arm if you desire to master the Bertholy Method. The considerable time I spent doing Deltoid Lifts was well worth it. But doing the lifts is thankless, tedious effort. When my left arm became sufficiently powerful and neuro-muscularly conditioned I could play a credible game with that arm alone and could hit all of the clubs in my bag. Driver distance was about 190-200 yds. overall with 7-iron about 115 carry. With both hands on the club my distances were about 30% greater.
Note: Paul Bertholy never advocated nor encouraged hitting balls or playing golf with only the left arm. In fact, he liked to tell the story of an experience he had at a PGA teaching clinic in which another renowned instructor was lecturing about the evils of the right hand and arm. The guy said that the right arm was a cancer. Bertholy replied that if the right arm were a cancer then Paul would gladly play him a match for any amount of money if the colleague would only use his left arm while Paul would use both his left and his malignant right. Paul said that his comment got a lot of laughs but his point was made that the right arm is not a cancer; rather, it is a wild horse which must be tamed in order to be useful to its owner.