Here is the problem: You need two things to activate sa 2 and they are using taunt and hitting enemy with blockbuster. The main porblem is you only have about 15 second window to hit enemy with your blockbuster and that is it. After the armor is expired, you won’t have other ways to proactively use your sa 2 until taunt’s cooldown is done. Epic sax, on the other hand, does not have this issue of using taunt and use blocbuster before armor expire stuff while dealing damage consistently throguhout the match. Also, epic sax can get regens and other buffs that increases his survivability other than having 1 or 2 stack of armor that lasts 5 second when hit. The versatility and flexibility of epic sax literally out matches the clumsy and rigid play style of heavy metal even considering the stats.
Also, i know it sounds funny but thats all folks counters heavy metal