Started playing Dragon Quest 6 on the SNES with a fan translation and i'm around 10 hours into it. Compared to Dragon Quest 11 it's far more unforgiving. The first major story boss has you going through a big, confusing dungeon with lava that damages you (and you have to walk on it to go through certain stairs), with enemies that can deal high damage, and at the end of the dungeon you have to fight that story boss twice in a row with no healing in between of any kind.
By the way, when you are in last portion of that dungeon, you can't even leave to heal yourself at an inn and save. I got fucked by my only character that can revive party members getting killed by a insta-kill spell. I pretty much just did a death warp by letting myself get killed by monsters, so that you could heal and save.
Defeating that story boss unlocks the job system and that has helped toned down the difficulty. But some story bosses can still be ridiculous in terms of damage output.
Read recently that apparently people complained that Dragon Quest 4 and 5 were too easy, and the creator of the series decided to crank it up in the sixth game by upping the encounter rate and beefing enemies. Which makes the overall lower difficulty in the DS remake of the sixth game kind of ironic.