i have been thinking for a long time the best IV's for him and i find out -spd +atk might be the right way, he have 51 hp with his new refined yeah his defenses sucks big time but with that high hp you will need to do a suicide move to get him kill with that 68 mixed bulk(17 for both stats unmerged) -spd doesnt hurt him at all because he have 41 spd with his new refinement and you doesn't lose bulk if you add fury instead of LnD 6 it can be really nice let me know your toughts
because unlike Karla and Ayra he doesn't benefit too much from spd to boost it more with 44 spd and 46 if you summoner support him with arena bonus 50 spd is more than enought tbh i mean with -spd he can reach 50 spd for the next 2 seasons in arena with a SPD bane and that's with fury on A skill instead of LnD, or 56 spd is needed idk i never fought anyone with 51 spd in arena O_O
What kind of armor team use visible buffs anyway? I never been in tier 20 nor 21 but I'm sure that armor emblem use Ward to stuck defence and resistance.
It's up to you to decide but I don't think you need that much hp, 57 will suffice.
Also he needs desperation. I'm sure he can survive through one hit not two. Even with special activation he will never kill with just one atk.
If you only plan to use him during Arena Bonus, then yes, I actually agree that -spd is optimal. Just with all the bonusses, you still hit 50 speed, which is normally enough to double anyting. Especially considering you will likely be able to boost it with some random rally spd/res. Honestly, 53 speed should always be enough, in Arena, especially considering that you can avoid enemy buffs if you have half a brain.
However, if this is your sole reason to use him, thn why not just use one of the Askr trio? Investing so heavily into Lon'qu should mean you'd want to use him in other areas as well, in which case, you'd want to merge him, and -spd may not be optimal anymore.
Fun fact, I posted another Lon'qu build for which -spd+atk may also be the optimal IV. It's very similar to yours, but uses Reprisal inste of Aether for guarantueed lol hits every turn.