The wattage listed on the antenna package refers to how many watts of power the antenna can handle as input.
.If your radio puts out 4 watts of power, the antenna will output approximately 4 watts of power. The "techies" will nitpick and say the 4 watts of output from the radio will mean the output from the antenna will slightly, very slightly be reduced to below 4 watts. Okay, not everything is 100% efficent. There will be a very slight percentage loss of power in the real world; but, for all practical purposes 4 watts output from the radio is 4 watts output from the antenna.
In simple practical terms: what you input to the antenna is what you get out. There ain't no way you input 4 watts to the antenna and the antenna ouput is more than 4 watts. Never going to happen.
I recently installed one K40 on my four wheeler. Light on the radio was red. SWR maxxed. I tried to tune it a little and nothing. After digging around, I find the factory end on the coax is messed up and a direct short. I cut it off and solder a new one on. It does work now but not real well. I need to bring the whole set up to a cb shop and have a pro look at it. Not much here though in the Green Bay area.