Sounds like you have a default of MTD with your TA and that's what they booked for you on initial cruise booking. While they may have access to booking MTD times, booking dining times may not have been open that far out - expecting them to keep looking when it opens and booking that for you is a bit much. Now, if you told them to book you in early traditional and they didn't do it, that's on them.
BTW, don't try to figure out why RCI does anything related to IT (likely the reason for your cancellation) - it just leads to frustration.