We agree that prices and wages will fall when money supply falls.Falling prices are only good if wages remain high and do not fall.
These good falling prices occur because of increased efficiency in production. New looms make clothing easier to produce, more clothing is produced, price of clothing falls. New agricultural techniques increase yields, price of food falls. And so forth. Fundamentally, the price is reducing because the supply of that particular commodity has increased, and price drops due to increased supply.
If wages remain at the same level, while prices fall, purchasing power has increased - the average person in society is now wealthier, because they can buy more things for their annual wages.
However, if the quantity of money available per person decreased, both prices AND WAGES will fall. People will not be able to buy any more than they could before. There are no "good effects" from this.
You have correctly described effects of productivity growth in second paragraf and third paragraf.
You are assuming both effects won't happen at same time. This is incorrect. Nobody will stop their productivity efforts just because money supply falls. So both coming together means prices falling faster than wages which means purchasing power going up.
Purchasing power = wages / prices. If wages falls by half and prices by quarter then purchasing power in now = 0.5/ 0.25 = 2. Puchasing power is now doubled.
Greater productivity means more goods are created. Looking from perspective of whole economy more goods implies more different goods because different people want different things. Some want cars, other phones. In the end more business will exist. And since workers are most flexible factor of production workers will see increased demand which will cause higher wages.