You never really need to level grind in this game. I haven't watched your Zeromus fight yet, but I've beaten it around level 45 (mind you, only Cecil and Rosa were alive, and utterly dependent on perfect command input). Things you don't appear to be aware of from the movies I've watched:
You should not attack with rods. Go to item, press up, then double click on a rod to cast its magic. The normal rod uses magic arrow, elemental rods cast level 1 elemental spells, etc. With a single exception (turtle), this magic is always stronger than these weapons' attack when they're relevant.
Monsters have rows in this game! Don't waste your physical attackers on back row targets when you could be killing the front row first. You could've been one-shotting a lot of enemies with counters if you were wiping out the front row first.
Equipping two of the same claw on Yang has no benefit. Always have two different claws on him. As long as you're hitting an elemental weakness, an enemy's elemental resistance/absorption is ignored.
There are items hidden in pots and the grass in just about every map.
There is a small room on the right side of Damcyan castle's exterior with some useful equipment and items.
Alligators are weak against ice, not lightning.
You can heal for free in chocobo forests (heal with magic, then restore your MP).
We have EVEN MORE themes now, but some old ones are gone...