I got a ton of gems (seriously, if scalps would drop I could make every weapon) but not a single hero or warrior's streamstone from the tempered event. RNG sucks. Your best bet is gold box investigations if it works like the rest of the monsters. At the moment the only way to get them I imagine is to tail Jho and farm tracks but I don't know for sure.
For the GS I don't know. I'm running with a Crit draw build instead of True Charged Slash and that seems to be working ok. (Haven't tried against TEDs though). Skills are Crit Draw, Earplugs, Quick Sheath, Weakness Exploit, and Handicraft. With those you should be doing a couple hundred damage each draw attack. TTS is still worth doing when the opening presents itself but draw attacks hit plenty hard when you can. If you still have Deco room I'd run some defensive skills.