Sorry but I tried Nak Muay and it really feels like the worst class in whole swordman tree now.
The skills retained their AoE size but they don’t give any extra AoE atk ratio and all of them depends on AoE atk ratio. Using Centaurus cards and +AoE atk ratio gears make you hit at most 5~6 mobs which is a riddiculous amount compared to most skills in Re:Build getting super high +Aoe atk ratio bonuses or fixed targets count instead.
The damage is also super low even when considering the dps against a single target. The damage is riddiculously low when compared to Highlander’s Skyliner that deals 416% * 4 against bleeding targets or even Moulinet that deals 312% * 5 against targets with Crown debuff. Not to mention the SP cost is riddiculously high for a skill that requires constant spamming to deal any damage. Highlander is just a superior option in every aspect.
As to answer your question, Muay Thai buff is mostly for killing bosses and provides a nice burst when doing so. I think it’s the best tool in Nak Muay class and deserves to be maxed. Taking out a few points from the damage skills doesn’t lower their skill factor as much as those extra seconds can provide when using the buff. Do note however that it’s a still lackluster skill with a lot of cooldown and will be mostly wasted if you (for example) get knocked back by the boss without pain barrier on. It’s also very SP intensive and will most of your SP during those 15 seconds.