Hi. In general such delays are due to long job queues. The reason that create and update would behave differently is that create must happen via the Metadata API -- which is more subject to these queue issues -- and update can happen via the Tooling API which tends to have much shorter queues.
You can confirm this by
enabling debug logging for Metadata Deployment and Salesforce DX and reproducing the issue. The resulting idea.log should show exactly where the time is being spent. I'm happy to take a look if you'd like. You can send your idea.log file(s) to
sup...@illuminatedcloud.com for review.
Assuming this is queueing, you would need to log a support case with Salesforce. Generally once such an issue is brought to their attention, it tends to get resolved pretty quickly.
Regards,
Scott Wells