There are close to 300 posts on Flyertalk.com regarding Concierge issues at Marriott's all over the world. I experienced a similar issue last month at check-in at the Marriott Hartford Rocky Hill, CT. The confrontation at the front desk was so negative it prompted calls to all the full service hotels where I have upcoming reservations to make sure that I would not have a repeat experience. Several hotels reduced services, so I rebooked reservations with hotels claiming that the Concierge was open or provide breakfast vouchers. After reading about your experience, I am extremely concerned about having to rebook reservations all over again. What a mess! Apparently, Marriott has no clue how much planning, time and aggravation this situation imposes upon loyal customers.
According to Marriott Concierge on Flyertalk.com, Marriott is indeed reducing operating costs to meet target bottom line numbers, but hotels are instructed to do so in ways that are non-guest facing. It's very clear from our common experience, that the failure to deliver is most definitely guest-facing.
You did what I would do in rebooking. Thank you for sharing your experience. I prefer to be warned, than not.