How exactly do we define something as "Overpowered"?
1) Do we mean by the gun's performance exceed its limited duty like breaking the rule of Sniper > Rifleman > Pointman > Sniper?
2) Or do we mean the gun outclass its own class significantly? Like M4 MK.3 obviously outclass M4 MK.2 where it was top tier gun in the past.
I would say it is overpowered if it satisfy both 1) and 2) category, guns like SA58 para, Desmodus and if one day we have a fully automatic sniper that can hip fire where it keeps sufficient capability in long range, then it will be overpowered.
In my opinion, I own the Striker-12 as well, and I think its 1 hit kill rate is not as great as Saiga-12, SPAS-15, it's just the reason you can quickly pull another shot on the enemy to make that up, whereas other shotty has to wait for the kock cool down to fire another shot, it becomes a sprayable shotgun in other words, which is a little bit overpowered in my opinion, but I would only reduce its ROF if I were to. I was bored with how the Striker makes everything so easy as well, so I grabbed my Saiga-12 for fun, and it's definitely still very good as well.