AmEx cards can be churned but you need to wait 2 years btwn CC closure and re-app. This has worked for Delta and MR cards.

You can also check out more guidelines on churning.

This is a general rule, i.e. from anecdotal evidence and not confirmed by AmEx. So go forward at your own risk.

I would agree that diversification is a beneficial and Chase Sapphire/bold are great cards.