Quit subjectively labeling a shot as being weaker or stronger. If more than 70% of the top men use a two-hander, it must not be the totally whacked out shot that some of you seem to believe it to be.
However, from my standpoint, a teaching pro of over 30 years and having trained well over 3000 players, the two-handed backhand is the superior stroke for developing a solid, effective backhand. Most players who have weak or very inconsistent one-handers can use the two-hander to learn new patterns and even discover something new about the backhand. Trying to continue to fiddle with a flawed one-handed backhand will only result in the player reverting back to their flawed form...because it is too close of a swing pattern to their bad technique.
You will never develop a worse backhand if you try a two-handed stroke with proper technique. You can, however, discover something new and productive with it.
Author, Tennis Mastery & Coaching Mastery