Edson Drake
Good news everyone!

Hiya. I actually have an Elysion too, and was planning to build around it, but was waiting to see if a level cap rise would be announced before putting the 7 S-ATK on my mag. And it was! Whaddya know, eh? Anyway...Elysion and Sazan 16 were the "best" (really, most practical, never truly the end all be all set up) up until SHAQs hit. In AQs, the most important thing is PSE bursts, and Sazan does not help you anywhere that doesn't feature enemies weak to wind. I, and several others, strongly suspect, but lack confirmation, that PSE triggers more frequently if you target an enemy's elemental weakness(es).

Whether that's true or not, however, Elysion still has shortcomings. It's abysmal on any tech that isn't good uncharged. Ilfoie, Nabarta, Ilbarta, Sazonde, Sazan, and Namegid are it. Every other tech, you want something else to use with it (besides Razan, but nobody uses that for damage). If you want to Zondeel, you want a Talis to be able to support party members. If you want to Nafoie, you want a Rod (preferably Bert Rodan). And so on. Elysion is only worth using for those techs. You'd still get more damage using Bert Rodan for Ilfoie, or better Namegid mobbing off a Talis Zondeel, but Elysion has very useful applications for the techs nonetheless.

Now, for an actual build? If you have one skill tree, you basically have to do general purpose. The absolute best way to play a casting character is having multiple skill trees to max out Masteries. Otherwise, you're just stuck trying to balance things out. You can focus more on Lightning/Dark if you want to, but don't try to min-max. You can't do that with one tree. It's unfortunate, but that's how the class was built. It is a good idea to try to get the best equips and such anyway, though. Best way to calculate that kind of stuff is to take your T-ATK (counting weapon and affixes, other modifiers as well if you want), take your multipliers (multiplying all of them, including any potential and the 30% default JA bonus), and figuring out which weapons yield the best resulting damage from that. Like, Satellite Riser would be best for Lightning, but if you have Talis Tech Bonus maxed, then King's Bit outperforms it on Mechs. 'course, this only helps you determine damage, but you can probably figure out utility potentials on your own.