This can be answered either way using sufficient evidence. I will explain both sides of the argument below.
There are multiple theories of government. One being hyperpluralism that argues there are so many interest groups that government stops being able to function due to gridlock. If the American people become so divisive and have many differing interests, it becomes difficult for government to come to compromises and enact/execute legislation. Furthermore, many have supported the idea that amongst the educated and wealthier portion of the population, people are no longer pursuing political parties to meet their needs but joining interest groups instead. As a result, we have seen the proliferation of interest groups in America. For every cause (ie. pro-life) there is an interest group that forms and there usually is a counter cause (ie. pro-choice) interest groups that exists. This supports the idea that interest groups' influence may be an illusion since one interest group has the potential to cancel the efforts of the opposing interest group. Also, as mentioned above, there is evidence to support that those who belong to interest groups are usually well educated so they may not be a true representation of the American public. Lastly, two significant factors contributing to the success of an interest group is their ability to organize and raise money. As a result, it may not be the case that all active and legitimate interest groups can make themselves heard.
On the other hand, interest groups are a linkage institution meaning they link or gives access to the American public to activism. Interest groups, if organized well, can pursue numerous avenues to have their voices heard. They can raise a significant amount of money and form PACs or 527s and engage in electioneering activities that can give access to policymakers. They can lobby all branches of government to pursue favorable legislation via iron triangles or issue networks (Congress), lobby to assure favorable execution of legislation (Executive), and file amicus curiae briefs of engage in litigation (Judiciary). To put the power of interest groups in perspective, think of the NAACP and the Civil Rights movement. The NAACP lobbied all branches of government to pursue their goals. An example of this coming to fruition is the overturning of Plessy v. Ferguson in Brown v. Board of Education. This would certainly support the argument that active legitimate groups have the potential to be heard.
Hope this was helpful!