There is a Talmudic passage which paints an interesting picture about the relationship between Moses and Aaron vis-a-vis speaking to the people:
Eruvin 54b
ת"ר כיצד סדר משנה משה למד מפי הגבורה נכנס אהרן ושנה לו משה פירקו נסתלק אהרן וישב לשמאל משה נכנסו בניו ושנה להן משה פירקן נסתלקו בניו אלעזר ישב לימין משה ואיתמר לשמאל אהרן רבי יהודה אומר לעולם אהרן לימין משה חוזר נכנסו זקנים ושנה להן משה פירקן נסתלקו זקנים נכנסו כל העם ושנה להן משה פירקן נמצאו ביד אהרן ארבעה ביד בניו שלשה וביד הזקנים שנים וביד כל העם אחד נסתלק משה ושנה להן אהרן פירקו נסתלק אהרן שנו להן בניו פירקן נסתלקו בניו שנו להן זקנים פירקן נמצא ביד הכל ארבעה מכאן א"ר אליעזר חייב אדם לשנות לתלמידו ארבעה פעמים וקל וחומר ומה אהרן שלמד מפי משה ומשה מפי הגבורה כך הדיוט מפי הדיוט על אחת כמה וכמה ר"ע אומר מניין שחייב אדם לשנות לתלמידו עד שילמדנו שנאמר ולמדה את בני ישראל ומניין עד שתהא סדורה בפיהם שנאמר שימה בפיהם ומניין שחייב להראות לו פנים שנאמר ואלה המשפטים אשר תשים לפניהם וליגמרו כולהו ממשה כדי לחלוק כבוד לאהרן ובניו וכבוד לזקנים וניעול אהרן וניגמר ממשה וליעיילו בניו וליגמרו מאהרן וליעיילו זקנים ולילפו מבניו וליזלו וליגמרינהו לכולהו ישראל כיון דמשה מפי הגבורה גמר מסתייעא מלתיה
Our Rabbis learned: What was the procedure of the instruction in the oral law? Moses learned
from the mouth of the Omnipotent. Then Aaron entered and Moses taught him his lesson. Aaron then
moved aside and sat down on Moses’ left. Thereupon Aaron's sons entered and Moses taught them
their lesson. His sons then moved aside, Eleazar taking his seat on Moses’ right and Ithamar on
Aaron's left. R. Judah stated: Aaron was always on Moses right. Thereupon the elders entered and
Moses taught them their lesson, and when the elders moved aside all the people entered and Moses
taught them their lesson. It thus followed that Aaron heard the lesson four times, his sons heard it
three times, the elders twice and all the people once. At this stage Moses departed and Aaron taught
them his lesson. Then Aaron departed and his sons taught them their lesson. His sons then departed
and the elders taught them their lesson. It thus followed that everybody heard the lesson four times.
From here R. Eliezer inferred: It is a man's duty to teach his pupil [his lesson] four times. For this is
arrived at a minori ad majus: Aaron who learned from Moses who had it from the Omnipotent had to
learn his lesson four times how much more so an ordinary pupil who learns from an ordinary
teacher.
R. Akiba stated: Whence is it deduced that a man must go on teaching his pupil until he has
mastered the subject? From Scripture where it says: And teach thou it to the children of Israel. And
whence is it deduced that it must be taught until the students are well versed in it? From Scripture
where it says. Put it in their mouths. And whence is it inferred that it is also his duty to explain to
him the reasons? It has been said: Now these are the ordinances which thou shalt put before
them.
But why did they not all learn direct from Moses? — In order to give a share of the honour
to Aaron, his sons, and the elders. Then [why was not this procedure adopted:] Aaron might enter
and learn from Moses, his sons might then enter and learn from Aaron, then the elders might
enter and learn from his sons and these finally might teach all Israel? — As Moses learned from
the mouth of the Omnipotent his own teaching was of greater value. (Soncino translation, my emphasis)
According to this interpretation, Moses taught everything directly to the entire nation, and then everything was repeated to the entire nation by Aaron (and then by his sons and the elders). The Talmud specifically points out that it was important for everyone to hear everything (at least once) directly from Moses himself, and not merely through Aaron as a mouthpiece/intermediary/interpreter.
