That is not a realistic analysis, if that held true (and I do it debate the merit of this particular claim) then only the next data point can be predicted with an edge. That is not what trading strategies aim at, predicting only the next data point, after all you don't look for holding periods of seconds. Higher highs and lower lows hardly predict with any edge whether a trend continues for another 50 or 100 basis points or even just 20 basis points to overcome the cost of execution.
In practice this is just not true. Once price has established a trend, the least likely thing it will do next is reverse. That behaviour alone provides an edge.
Of course, price in a trend doesn't just continue in a straight line, but some form of continuation is the most probable early outcome at any specific point selected within the trend.