Klarna is a bank that is connected to the Visa network. So, inherently, it is bound by the same rules as any other bank. So, in the context of this thread, they are not a competitor to Visa/MasterCard.
That's correct only in NA, where Klarna issues virtual credit cards and transactions happen via card tracks. In EU, or at least the Nordics, the transactions are bank-to-bank and there is no virtual card. That means they are a direct competitor.
In Sweden they issue regular credit cards (my friend has one).
Also, AFAIK, in Nordics they offer virtual card payments to merchants who don't integrate with them directly.
Sure, they have plenty of collaboration with both major card schemas. AFAIK, they do both acquiring and issuing. I don't think collaboration means that you can't compete with each other? Their most successful products in the EU are not using card tracks.