You got it!
I use the Citi Hilton Reserve card to MS my way to $40k... I feel that Citi has less opportunity for closure. Amex is so FR happy that you could risk your accounts being closed.
Just make sure you let Amex push 2018 Diamond status to your HHonors account before closing the card. Once you have the status, Amex will not take it away since you qualified for it and your account has already been upgraded.