I just checked out both Disgaea and Demon Souls and wouldn't say they are competing with FFXIII-scale JRPG games. Demon Souls looks like a WRPG - you create the character, there is only one character you control (who makes up your entire party, it seems) and that character does not really have an in-depth storyline or anything. I would say Demon Souls is competing with Oblivion, not Final Fantasy. Disgaea (which is a pie SE has it's finger in already) is definitely a JRPG but is nothing people would directly compare with FFXII, FFXIII etc.

I imagine The Last Story will be the direct competition that FF receives. Unfortunately, it's only on the Wii.