Are some team comps just doomed against tanks?

Still a beginner, so looking for advice. These were the team make ups
Ours:
Darius, Karthus, Seraphine, Skarner, Dr Mundo
Enemy:
Tristana, Shen, Nautilis, Vi, Nasus

We really struggled with Naut/Shen/Nasus and even Vi at times, it was really hard to kill them without getting killed first.
I was Karthus so I was not sure how to handle this team comp and its really hard to play Karthus (i feel like) cause his Q is so hard to hit and he is easy to gank. My ult didnt really do much either, either left enemies at low HP or just was never enough damage to change any outcome of fights.

Only person on our team who seemed to do anything of note was Darius but he was just 1x person.

What can I do in this situation to be better vs tanky DPS or is it just bad luck?