Which mage class is worth to invest empress set on?

I would go with what Green4Ever said but based on your line-up I would say Luminous is the best choice pure variety wise while BaM would win out if you like playing support as well since BaMs become really powerful when they get their Hyper Skills and are pretty much indestructible too.

Yeah, I knew that BaM is a beast in party support since i have one lvl 15x, but just spamming similar skill (Finishing blow) throughout the journey is rather repetitive, and i believe no one will use battlekingbar except for bossing, and i seldom go bossing since my fund does not allow me to do so.

Lumi is kind of OP now (all new classes are OP anyways). I don't know if it gets nerfed to dust like DS though, so its a risk.

That would be a 'No' if we base it solely on KMS' Luminous nerf but I do think that it's no longer safe to plan solely by that seeing that CMS' Angelic Burster is already being nerfed even worse than her nerfed KMS counterpart before being released. I would say that if the OP is concerned about that BaMs would be a better choice because they've only been made better and better.

Yeah, luminous did not get a serious nerf in KMS, so i may considering main and fund him. I really enjoy playing him.

That's why he/she should make one!

I am not considered to make another adv mages since i already had an I/L, although F/P is god in dps-wise.

Thanks everyone for the suggestion. I really appreciate it.