A VERY astute question and well put too:thumbsup:
**CONDITIONALLY
God would forgive that person on the spot. IF [a really BIG IF] **contrition is sincere to the point of with God’s future grace to amend one’s life style [action not just words] to avoid sinning that way again.
HOWEVER:
Because of the God imposed conditions; one MOST often would be wise to at least wonder if they had met God’s conditions sufficiently for God to forgive or not to forgive them. PERFECT contrition is the requirement; nothing less than.
Sacramental Confession is the KNOWN forgiveness of man’s sins Mt.16:19. And there is always [with contrition [even imperfect] grace attached to this Sacrament.
I edited your post so that I can respond to as many of your points as space permits.
**God can and does but critically conditional **
. .
Your on safe ground here but again it is highly cognitional.
Isaiah 55 comes to mind
"**Seek ye the Lord, while he may be found: **call upon him, while he is near. Let the wicked forsake his way, and the unjust man his thoughts, and let him return to the Lord, and he will have mercy on him, and to our God: for he is bountiful to forgive. For my thoughts are not your thoughts: nor your ways my ways, saith the Lord. For as the heavens are exalted above the earth, so are my ways exalted above your ways, and my thoughts above your thought
Friend what is missing from your example is critical to what God intended for this Sacrament; and not to anyway the same degree without it.
Jn 20:1-23 edited for space
Now when it was late that same day, the first of the week, and the doors were shut, where the disciples were gathered together, for fear of the Jews, Jesus came and stood in the midst, and said to them:
Peace be to you. And when he had said this, he shewed them his hands and his side. …
He said therefore to them again: Peace be to you. As the Father hath sent me, I also send you. When he had said this, he breathed on them; and he said to them:
Receive ye the Holy Ghost. Whose sins you shall forgive, they are forgiven them; and whose sins you shall retain, they are retained".
What is missing from your example is:
- Absolute Certitude of forgiveness
- Know and assured forgiveneess and with it God’s fulfilled desire for OUR Peace:thumbsup:
- The Grace and indwelling of the Holy Spirit [assured in Sacramental Confession} NOT assured in seeking directly God’s forgiveness.

ALL sin has what we might term a “public nature”; meaning all sins effect others besides the sinner themselves. Sin therefore accrues a directly God-imposed penalty termed “the Temporal Punishment” for our sins which too must be repaid before one can enter into he Beatific Vision. Only perfect & perfected souls can attain heaven…
Your understanding of God’s Justice is very good.
The differences Going Directly to God AND OR; going to what God has Directly and Precisely-Ordained as HIS NORM for the forgiveness of sin is PROFOUND and critically important. .
The sacraments all exist for our benefit; God being Perfect cannot be mad more-so. So assume some sort of right to bypass God’s Plan for man’s salvation is not a wise choice. In an emergency; ABSOLUTELY! As a freely chosen exclusive practice; NOT such a good idea. we are NOT to challenge God’s desires; by choosing what makes US “feel good.”
GREAT post