I would disagree, that the character Tom Cruise portrays could not learn such swordsmanship in 6 months. It was a bit fast, but consider that he is a verteran of more battles than most if not all of the Samarai. He was already pretty much an expert with his calvary sword, which would require just the learning of different techniques versus not knowing anything about fighting at all.
Remember the scene in which he gets into a draw while training because he finally figured out a diferent mindset. The movie emphasized that he was already a great and formidable fighter, but "learned" how to be Samarai. It wasn't about some stupid peon suddenly sprouting samarai wings.
As the "last" samarai, it was not Tom Cruise. Although he learned their ways (and was maybe better in some ways), he was NOT samarai. The last one committed seppaku (sp?) on the battlefield with Tom's help. I think the movie pushed how Tom's character only saved himself because of Samarai values, but the irony was that there was no more room for the Samarai.