True Hero: Frodo or Samwise?

[Lotrelf]

This is from one of the letters by Tolkien.

By chance, I have just had another letter regarding the failure of Frodo. Very few seem even to have observed it. But following the logic of the plot, it was clearly inevitable, as an event. And surely it is a more significant and real event than a mere 'fairy-story' ending in which the hero is indomitable? It is possible for the good, even the saintly, to be subjected to a power of evil which is too great for them to overcome ¨C in themselves. In this case the cause (not the 'hero') was triumphant because by the exercise of pity, mercy and forgiveness of injury, a situation was produced in which all was redressed and disaster averted. Gandalf certainly foresaw this. See Vol. I p.68-69. Of course, he did not mean to say that one must be merciful, for it may prove useful later ¨C it would not then be mercy or pity, which are only truly present when contrary to prudence. Not ours to plan! But we are assured that we must be ourselves extravagantly generous, if we are to hope for the extravagant generosity which the slightest easing of, or escape from, the consequences of our own follies and errors represents. And that mercy does sometimes occur in this life.

Letter 192, The Letters of JRR Tolkien

Going beyond the words of professor isn't bad. It's just, you think differently than him.
I never really understood why would he say that Sam was his "chief hero" only because without him Frodo would have failed? Makes no sense to me. Among all the characters it is Frodo only who suffers most and sacrifices most. And not even gets the wanted "happy ending" i.e. Peace in his homeland and ends up leaving it for ever. Didn't Tolkien acknowledge any of this?