Ok before I make this statement let me say I am also a "vetren" myself, as I was around during the time of ladder points

Mythicals (in my mind) are a way to enhance gameplay, while still helping Tactisoft, the company that owns SuperMechs, turn a profit.
Don't get me wrong, there are a lot of mythicals out their that are better than their legendary counterparts. But the ones you describe need special circumstances to truly be overpowered.
Needle Blaster Mk 2 (I know what Im talking about, I own 2)
- You need two of them
- You need a torso with high base heat (Lavascope os the only option)
- You need 2x Bullet Packs (preferably +70)
Red Rain Mk1 (I also own this)
- You need at least one rocket pack
- You need a torso with high heat and energy (UltraSpade)
So what Im saying is that someone who owns these weapons also needs more items to create a mech that would be classified as "overpowered".