So what I'm getting at is that there is no reasonable chance for the driver to incur a loss as they do not have any fixed expenses the are required to pay even if the vehicle is not generating any revenue.
The definition of an independent contractor is not a clear as you are making it out to be, and it is not determined by one item alone on whatever list of independent contractor characteristics you are using.
The IRS uses one list. Each state has a list of its own. Courts have made different decisions based on essentially the same set of facts but in cases that have their unique nuances.
If this issue was cut and dry, there would be one list that everyone used and agreed upon. Also note that the definition of an independent contractor for tax purposes may be different than the definition for unemployment insurance purposes. There is much to consider.
The definition aside, it is indeed possible that the driver of a fleet owner's truck on a percentage contract can suffer a loss. It costs them money to be in business, like owner-operators.
The expenses are less because the driver is not paying for the truck, and maybe not for fuel, but it still costs the driver money to be in the business. Losses are not tied to loads. They are tied to the costs of doing business.
Driver expenses include the money to get and maintain a CDL, drug tests, office supplies, postage and shipping, truck supplies (paper towels, window cleaner, hand soap, etc.), work accident insurance that the fleet owner may not pay, orientation fees if the carrier charges them, cost of travel to mandatory training events, cost of lodging when the truck breaks down, internet access, business books and publications, business computer programs, self-employment tax, tolls if the fleet owner or carrier does not pay them, copy and fax expenses, highway use tax, truck repairs paid by the driver if the driver is at fault for the damage (if a driver leaves a perfectly good set of emergency triangles behind after using them on the road, the driver would likely pay to replace them), transponder fees, car rental for business purposes, tools purchased for use on the road that the fleet owner does not provide (bolt cutters, hand tools, a certain kind of dolly you want but that the fleet owner will not provide), driver's portion of a freight damage claim, drivers portion of the cost of an accident in which the driver was at fault (per fleet owner's contract), border crossing fees, business meals (you pick up the tab for lunch with someone with whom you meet for business reasons), taxi, monthly Qualcomm fees, driving glasses, work gloves, coveralls, steel-toe shoes, hard hat, safety glasses, uniforms if your carrier has them, scale costs, traffic fines, laundry, showers (occasionally paid for apart from free showers with fuel purchase), hotel when you want or need a break from the truck, dog food for the pit bull you keep in the truck for security reasons, truck parking, laptop computer, prepaid legal, fuel additive that you believe in but your fleet owner does not, DOT physicals, cost of attending industry events like the Expedite Expo, cell phone usage, TWIC card application fees, HAZMAT endorsement fingerprinting fees, passport cost, loss of damage deposit or earned pay to an unethical or incompetent fleet owner, and more.
Not all of these costs are deductible but all would be included as items on a driver's profit and loss statement.
