The key to longivity of any trading system is the application of fundamental trading principles used by the market makers.
There are many theories about how the market works with many day traders feeling that many market makers in bed with some brokers just run their stops.
There could be an element of truth in that depending on who your broker is and the trading method you are applying.
For a system to have longevity it must adopt fundamentals of the market makers, the market makers are not in business for the short-term their goals are long term and so must be your system. This writes off the News trading system as "not such a viable long-term system". In fact it is on the border of gambling.
There is the one aspect to the news system that is viable, such as the predictable buy/sell towards the news publication, but the question is how viable is this approach long-term. Make no mistake the human nature is to get nervous about some impending news or situation which explains why the inevitable price movement around news time but this doesnt make it a viable long term trading approach.
A viable system:
The final point is where most makers of systems disagree.
The real test is whether the system makes profit going in the direction of the market or whether it just happen to make profit by chance.
Nice thoughts there. I do feel that there have been too much emphasis on market makers in the world of fx trading that a lot of traders loose sight of the most important element, which in my view is money and trade management.
Traders can generally loose, whether they are the big banks or the retail traders. The major thing that separates the big banks and market makers from retailers isn't so much about their ability to move the market but about money management. There are many systems that are available out there that are good, but the problem is often with the emotional side of trading which makes traders either become too greedy or too fearful. Any system with just over 50% win ratio but with strict money management is a potentially profitable system.
I do think that risking 5% of account size on a position or me is too risky.