If there is a guest present, the guest recites the grace so that he will be able to bless his host. Therefore, if a younger person recites the blessing before the eldest or before the guest, the amount of the penalty will depend on the answer to the above question. If the ten gold piece penalty imposed by Rabban Gamaliel was because of the precept and not the blessing, then the penalty here would also be ten gold pieces and no more. However, if it is the value of the blessing, then, since the Grace contains four blessings, the penalty would be forty gold pieces. The Talmud comes to the conclusion that the penalty is for the loss of the blessing.
Evidence is cited from the following account.
This shows that your argument is false. I wish to research the matter. Then I will give you a reply. For the next three days, Rabbi Yehudah fasted, praying to God to help him against that heretic. On the third day, he was sitting down to break his fast and he had begun to recite the HaMotzi over the bread.