I recall addressing this on another thread some time ago, but which one I don't recall. In any case, in summation, Orthodoxy understands original sin (the ancestral sin) just as the canon states it, that it needs removed, not expiated. It does not say that baptism pays for original sin nor that it is for the forgiveness of that sin, as it is not a personal sin and therefore does not need forgiven. It does say remitted--i.e. removed, as with the remission of cancer. The original/ancestral sin is a cancer upon mankind that needs removed.
In that case, I think you and the RCs are in agreement. They make it clear the "guilt" is not personal, but a shared consequence.
Also, "remission of sins" is a common term for the removal or forgiveness of sin in the Latin Church. The forgiveness then is not personal, but our state of "rejecting of God" in our generation.
I understand it in the context that we are born with a fallen nature. You can call it original sin, ancestral sin, the ancestral curse, or whatever else you want to call it but in terms of the Church being a hospital, we are born sick and need to be brought into the hospital for healing. We are born subject to sin and death, which is not God's intention, which in itself "misses the mark" set by God. Children are not born "guilty" of anything needing "forgiveness", but they are born subject to sin and death and outside of the Church, which is God's family. It is through baptism that we are united to Christ and the Church. The wages of sin is death, and it is through baptism that we die with Christ and are raised up with Him, so along with freedom from the original sin that we are born into we also receive forgiveness of past offences.
This state of "missing the mark" is the "sin" we are born into and share "guilt". The canon specifically addresses this, in that infants have no personal sins, but are still is in need of forgiveness.
But if baptism was nothing more than "forgiveness" for what you were "guilty" for, then the disciples of John the Baptist would not have needed to be re-baptized.
I'm not saying what happens to unbaptized children who die before they can be baptized and have committed no personal sins, they are in God's hands and we can pray for them and need to trust Him to do what is right.
It isn't the only reason. This Council was specifically to say the opposite, that is baptism wasn't only
for Church entry, as Pelagius claimed. Also, the next canon:
Canon CXI. (Greek cxiij.)
That the grace of God not only gives remission of sins, but also affords aid that we sin no more.
Likewise it seemed good, that whoever should say that the grace of God, by which a man is justified through Jesus Christ our Lord, avails only for the remission of past sins, and not for assistance against committing sins in the future, let him be anathema.
That is, baptism does three things, (1) we enter the Church, (2) we are forgiven all sins, and (3) we are given strength to persevere against future sin through the strength of God's grace.