Myrmidon* and yeah, Lon'qu is good. Generally it's better to cap at 20 before upgrading to an advanced class.
I would have suggested not using Frederick at all since he is OP early on but not actually that great so he just prevents other people from leveling. He is useful as a partner though, I used him to get Donnel through his early levels.
And the problem is you have to use Frederick early so other people won't level as much.
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