With the ongoing unification in the standards of education all boards have adapted almost the same course structure. So there is nothing to worry about. The difficulty level also has come to a common platform. But yes it is slightly tough to score marks in ICSE board as compared to other boards.
The number of subjects that one has to study is more as compared to other boards.
The focus of ICSE board is purely on academics as compared to CBSE whose focus is on holistic development of the child.
So yes it could be said that it is slightly tough to score marks in ICSE board. But remember hard work and determination is required to score good marks in each board.