realy low damage on tft

hi...i got 1 question...i have realy strong team (2 star mundo,neko,maokai,ivern,rexsai,kogmaw and warwick and 1 star malphite and taric)they win every thing...kog got blodthirster and guinso ragaeblade and fire biff before problem he made around 3 to 4 k dmaage...then last 5 games he did nothing.my damage drop amazin kog make 600 damage all other less...can u help me understand this?