If it is cheaper to go by car, that depends on how you compare it. If you travel 1 day a month, the train will almost certainly be cheaper because you don't have to buy the car and pay the taxes. If you travel a lot, a car _might_ be cheaper, but even then I doubt it. Don't forget that unlimited train travel in The Netherlands is roughly 380 euros. Is it extremely expensive? Yes. But depending on how often you travel through the country, it might be cheaper than a car.
Secondly, I complain about NS a lot about delays and about not being able to sit. I am not going to argue that it isn't a problem that has to be improved. During rush hour (and plenty of times, outside) it is sometimes impossible to find a seat. But, horrible unreliable? that is not how I would call it.
Along with that, don't forget that our train system is extremely busy. For example, the trains that go from Amsterdam Zuid to Schiphol is the 7th busiest station in the country and it has only 4 lines, all of them which are almost constantly in use. The moment anything goes wrong, that has a domino effect on all other trains.
Personally, I own a car and I use it quite a lot. But I also use public transport quite a lot. For point to point travel outside of cities a car is a no brainer, if you stay within the cities, it is probably not worth it to have a car.
Finally I want to point out that our train system has problems, it has delays quite often, there aren't enough seats, and it is expensive. These are all things that we really have to improve. But It is nowhere near as bad as you make it out to be.