Buying a bond from the issuer is investing. Buying an IPO is investing. Buying a rental property is investing. Investment implies possible productive result from the action. When you buy shares or bonds already on the market this just exits the previous holder, it does nothing productive.
I would define it differently. If you are putting money in something with the hope that the price goes up, that's speculating. If you put money in something with the hope that it generates income then that's investing.
So buying stocks could be either one.
And using it to generate income, maintaining it for the customers (renters) etc
Scenario 1: I hold all the stock for decades until I die. Under your terminology, I am the sole "investor". Fine.
Scenario 2: 1 millisecond after my purchase I sell everything I bought in the IPO to thousands of market participants. Under your terminology they are not "investors". I can't be an investor either, since I hold no more of the stock. Does the company no longer have investors?