Think of it this way: the switch you're adding inside the cabin is meant to make the winch circuit available, NOT to operate the winch. The winch has its own switch for that, whether manually at the device, or using a remote. The switch leg to the cabin is simply to tell the solenoid to energize the high-current circuit and make it available to the operator of the winch. You turn the switch on to make the winch available, and then operate the winch using its own included controls.
So the solenoid passes the high-current through it only when the low-current switch leg is "on". In that sense it's just like a relay, and acts as one.
But the responses above are correct that you need to see what the solenoid's switch leg current is, and make sure your switch is rated for at least that - it should be, but you should check.
Another reason to use a solenoid is that if you don't, that winch is available all the time, from outside the truck. A malicious actor with a paperclip could trigger the controls and turn your winch on. Using the solenoid and the in-cab switch leaves it completely disengaged unless that switch is on.