You'll have a bad time if you just drop all emails without DKIM. There are many large senders that do not care about well established email standards and you will drop important emails.
These are the same senders that are correctly configuring DMARC?
You said DMARC does not prevent email forgery. I simply corrected you on that and explained what DMARC does.
Setting a DMARC policy that allows unsigned emails is easier than configuring DMARC signing including key management. It's just adding a DNS record. Although large senders should of course do DKIM and it's not that hard either
But I'm not arguing with you about whatever Outlook did.