True, and even still illegals pollute the EC since they are counted in the census and included in the totals that determine how many members of the US House each state has. California probably has eight or ten members in the House due to their illegal population of several million.
Several other states with a high illegal population also have some House members due to the illegals.
Also states with low numbers are underrepresented as the distribution of the 435 House Representatives would be skewed towards states with many illegals. It likely costs quite a few states at least 1 or 2 seats in the House.