It is an old, old joke that every bike weighs 25 pounds...you can have a 15 pound bike, but you would need a ten pound lock to protect it, or you can have a 23 pound bike, and be safe with a two pound lock.
Any lock, of any weight, or any price, can be opened eventually if a crook has the right tools and the right skills. I don't know of anyone with a 15 pound or 16 pound bike that would leave that bike out of their sight...a $2,000 or $3,000 bike is simply too valuable to leave locked where you can't see it.
Folks who leave a bike for eight or nine hours a day at the same location day after day need a bike that looks as if it is worth $20....and it is not hard to make a "pro" quality 1985 road bike looks like it is worth $20, even if it still rides like a $1,000 bike.
By the way, in most cities, it may not make much difference whether you use a two pound lock or a ten pound lock. "Cycling Plus" editors found that the low-priced OnGuard Bulldog u-lock, weighing just two pounds, can NOT be opened with manual tools IF the "U" is filled properly (such as with the rear wheel, plus a large, beefy locking post). So, a $30 Bulldog can protect against manual tools just as well as a $100 chain weighing ten pounds IF the owner correctly uses the "Sheldon Brown" locking method.
Power tools? It is rare for crooks in the average town to use power tools. But, if a crook has the right power tools and knows how to use it, no lock is strong enough. Which is why you don't leave a $2,000 bike out of your direct eyesight.