Same here, one of the easiest RPGs that I've played to date was also Silva Saga-II. Those mercenaries sure were incredibly powerful and the fact that they auto healed after every battle made the game even easier. Heck, I even beat the last boss with them. But hey, I'm not compaining. It sure did make beta testing for it quite easy!
As for the hardest RPG, I'll have to say 7th Saga. The first half of the game is okay, but later on you seriously have to level grind a lot when reaching a new area or the enemies there will literally cream you in one or two hits (especially if they use magic, which they often do). Even with level grinding though, you still have to use magic or items to double your attack/defense (along with speed sometimes) during not only boss fights, but also random encounters. But overall, I still think it was a great game and beatable if you're patient enough. I've found that having Lux as the lead character and Esuna or Valsu as a partner made the game a bit easier, but of course you can play and beat the game with whomever you want (just make sure to have a fighter and a mage, blocking before attacking is also useful as it increases your strength during that turn).