I agree that in theory, a higher caravan to car weight ratio could increase the risk of a snake - however, this assumes that all other factors are equal, which of course they never are. The distribution of load within the car and caravan, vehicle speed, wind speed, whether you are towing up or down hill, vehicle suspension, tyre pressures and conditions are among many other factors that could have an influence.
Like Woodentop, I've been driving Passat estates for about the last decade and started towing with them in 2015. I would wholeheartedly recommend them for both towing and comfortable solo driving. Given that you have previous experience of towing a smaller caravan with yours, I personally wouldn't be too worried about towing your new larger van with it. Just be aware that there is the potential for it to be a bit less stable in, for example, strong winds and/or exposed locations.
Just as an aside, the worst snake I've ever encountered was whilst towing an empty twin-axle Swift caravan with a much heavier 4x4 Hyundai Santa Fe. I have no idea what caused it and am certainly not suggesting that any of the existing guidance should be re-written to reflect my limited experience - only saying that no general guidance can cover all car, caravan and location-specific combinations.