It depends on the potential of each coin. As I know, the market will decline after it is able to reach its highest point. I looked at the graph of bitcoin, it took at least 4 years to give the best performance at the highest price he achieved last year. If such a thing is true, then I think the argument that you give is also true and is likely to occur.
No one could correctly predict what would happen, anything is possible to happen, bitcoin has a rapid growth in 2017 and i guess no one had predicted it. It is too long for 2 years, maybe 1 year is enough to know if there are any increasing movement.