The best answer to this is “it depends.” Some individuals are clearly made less important by the committee system. However, others are made more important than they otherwise would have been.
In our current system, the members of Congress who are not on a given committee have relatively little power over the laws that deal with that committee’s area of law. This is particularly true in the House of Representatives. The committees do the real work of marking up and amending the law and the rest of the members of the House are more or less expected to vote based on what their party leaders say or what the members of their party on the relevant committee say. This takes some power away from those members.
However, the system makes each legislator more important in the areas of the committees that they are on. If the whole House had to consider each law, it is likely that only a few party leaders would have much input on any given law. With the committees, however, each member (particularly in the majority party) will have more input on the bills that come before their committees.
Thus, the committee system actually increases the role of the individual members of Congress in some areas while decreasing it in others.