I've never had a level where they weren't affected by the failure title o.0
What I like to do is find a dungeon (open and cancel the dungeons repeatedly to reset) that has trees as it's main item, small area, and few enemies. Put a failure title on it. Get a good ways into it where you can still one-hit the monsters, but they are much higher level than you. The trees in the level should have like 10k-20k mana in them most of the time (if you're at the point of beating the game with some grinding done). Then you use bottlemails to get the trees.
Well as you said, stealing is a bit different here. First you want to get Quick Attack(1) on your bottlemails. That saves them one turn while getting items. Bottlemails do have the highest stealing rate, so that's the character you want for it. What you want to do is lift the item from the enemy, then throw it yourself. Then you want to confine your bottlemail to it. Keep it alive for the three turns it has or w.e, and it will then "steal" the item
It tells you the % chance you have at keeping it when you confine it, so keep that in mind.
I wouldn't worry so much about stealing items, rather than going to a high level failure-dungeon and just taking items around the level.
(1) This ability is the one to wich you were referring. Quick Attack lets you act right after confining. This ability appears on these characters.
[*]Ash (level 1)
Fenrir (level 1)
Archer (level 1)
Werewolf (level 1)
[*]You can't use Ash for this.
What you want to do is make sure you have a fusionist. Make one of the aforementioned characters, get a lot of mana on the bottlemail (or other character you're giving this to), and fuse the created character to the bottlemail. When you do that, you can select skills on the character to give to the new one. That's when you will select Quick Attack. This takes quite a bit of mana to do.
If you need more mana, do the failure dungeon thing. Get an item with 10k+ mana and fuse it to your character you want to learn Quick Attack, but don't select really anything besides the stat upgrade. You'll get the left over mana.