You are wrong, for two reasons:
- You assume there is such thing as a total money amount. There isn't; rather there are measures of the amount of money flowing in the system.
- You further assume all money is available to buy all assets. This is not true. Although any dollar can be exchanged for any other dollar, it remains the case that depending on the distribution of money, not all goods and services produced can be bought. Capital reserves of banks don't count, for example.
If there is no credit and houses are worth a fixed 1000 dollars, and the median American has 900 available at any time, not all houses can be bought, and the amounts of dollars is worth all goods produced minus houses divided by the available money. Now, if you print money and give Americans each 100 dollars, suddenly, you have simultaneously increased the value of money and the number of dollars!
This is how stimulus works...