If you insert a letter, it implies that you have to delete and add a certain letter: (cost 2)
If you simply add or delete: (cost 1)
This is a well known approach called minimum edit distance.
I passed all tests but the one we are talking about.

e.g.
rkacypviuburk to zqdrhpviqslik, cost: 16 because you have to delete and add 8 letters
rkacypviuburk to karpscdigdvucfr, cost: 12 because you have to delete and insert 5 and also delete 2 letters

same account to the test you are addressing!

I solved the kata by comparing costs.
If you insert a letter, it implies that you have to delete and add a certain letter: (cost 2)
If you simply add or delete: (cost 1)
This is a well known approach called minimum edit distance.
I passed all tests but the one we are talking about.

rkacypviuburk to zqdrhpviqslik, cost: 16 because you have to delete and add 8 letters
rkacypviuburk to karpscdigdvucfr, cost: 12 because you have to delete and insert 5 and also delete 2 letters

Please correct me if I'm wrong!