Seat belts will give you a higher percentage of survival than if you didn't have it on.
The vast majority of crash studies have proven this a long time ago.
Want a 4 or 5 point harness, that's not a problem, just go buy one and install it in your vehicle, many people have. It will give you an even higher chance of survival with less risk of seatbelt caused injury.
Want even better chances, add the fire suit and helmet.
Going all the way, install a roll cage and mount a fire extinguisher within drivers reach.
Survival is about preventable risk, and it's up to everyone to make their own call, but take note, you will not find any race cars without the above noted safety features.
The professionals have way more knowledge of crash survival, if they do it, so should you.