This was an awful mastery due to being linked to ST only, this is not something you want from a tuning pov as it makes you need to carry different gearsets between ST and AoE situations which is a right pain in the rear.
Legion’s version as a talent was cool, however I also think this is a little vestigial.
Due to one reason alone… Slayer.
Slayer has follow up attacks in it’s procs of Slayer’s Strikes being practically this but renamed and with better effects attached to it alongside and AoE variant of Reap the Storm.
Now if we wanted to make actual oGCD ‘follow up attacks’ akin to FF14s Gunbreaker or Viper that could fit with Arms giving it a combo that you will hit inbetween some GCDs, but WoW’s GCD is a little too short without letting this get out of hand fast if they make the proc rate for it a little too good.