The Lenuses are dispatched pretty comfortably on the English version with attack item spam and/or Dart's fire magic. Mainly Burn Outs for the first fight earlier on disc two and Burn Out/Gushing Magma/etc for the second fight where she comes with the dragon. As NEB noted earlier multi target effects good stuffs~
On JP version the attack items are nerfed and the targets have higher HP, etc. In this case for the second Lenus fight it is two targets with higher HP/two separate boss targets, and they turn it back at you by them having the MT good stuffs, and they also act pretty frequently. Regole is more of a threat here since the one fight where I took Lenus out first Regole started seriously spamming his MT stuff so yeah. That time I ran out of Angel Prayers so I had to end the fight with Meru solo. Basically you are relying on your additions more, and Dart still has his dragoon magic, but you still have to get/take/etc enough turns for him to build up the SPs and you might be screwed if you forgot to bring MP restoring stuff (and you have to balance that with what healing, revival, etc items you need this time as well, and whether you want to spend your money on equips or items in general since amount of money gained after fights is nerfed in JP version as well) Then for ST MP restore you have to decide whether it is more important to restore Dart's MP or Albert's for defense on Rose Storm. No doubt the fight would have been even uglier without Rose Storm too.
You might be right, NEB. Fighting Grand Jewel with dragoons didn't seem too scary -
https://www.youtube.com/watch?v=PznyZHWHxwQ&list=PL0-L-Wk7FQUoBXA09O3CzfhO6lDRinjSk&index=51This was p comfortable win. Albert/Meru defensive combo p hard to break~