> Netflix, Uber, Amazon, PayPal, etc?
Not sure if Netflix was first to DVD by mail, quite possibly; they were early, and I don't know if VHS rental by mail was ever a thing.
Uber may have been the first to internet hail livery vehicles, but Sidecar was the first to do internet ridesharing as an app, and Lyft was the first to call unlicensed taxi service ridesharing. Uber is winning in the marketplace at the moment though and Sidecar is dead; of course, winning in this market still means burning money.
Amazon was early to selling books on the web, but e-commerce catalog sales were available on pre-Internet information services. AWS defined a new category of managed hosting, but lots of other companies did similar things before.
I think BillPoint may have slightly predated PayPal. Being early here seems to have had staying power, as Yahoo's PayDirect didn't do well enough to stick around. Otoh, Venmo was good enough to buy, Zelle seems popular, and other easy credit card processors like Square and such seem to be winning over that side of PayPal's market. There's a moat, but it's not very deep.
> Was Dropbox first to market? Did they win the market?
No, there was XDrive and Yahoo Briefcase and probably more that launched and shutdown before Dropbox. Not sure if Dropbox won, OneDrive and Google Drive are contenders still.