Disney's Resort Airline Check-in (RAC) used to refuse bags exceeding 50 pounds because they had no way to collect airline fees for such bags. Then most airlines imposed fees for most checked bags, and RAC developed a system to collect fees on behalf of the airlines.
There are still a bunch of unofficial websites (including WDWinfo and AllEars) that have the 50 pound limit in their RAC write-ups, but it's no longer on Disney's official website, at least not on the main pages about DME and RAC. In fact, Disney identifies "bags exceeding certain weight limits" as one of the fees that RAC can collect, which certainly suggests that RAC can accept bags weighing 50-70 pounds in addition to the usual bags weighing less that 50 pounds.
See
https://disneyworld.disney.go.com/f...ion-and-check-in/resort-airline-check-in-fee/
Q. Is there a charge or fee to check my bags at Resort Airline Check-In?
A. In general, the same baggage fees apply at Resort Airline Check-In as they would if you checked in at Orlando International Airport. Fees vary by airline, but common fees include charges for additional checked bags and bags exceeding certain weight limits. Ask your airline or check their website to learn which fees may apply to you.
To pay airline baggage fees, please call Baggage Airline Guest Services at (407) 284-1231 to pay the fees before visiting the Resort Airline Check-In desk. Guests under 18 years of age must have parent or guardian permission to call. You can pay baggage fees with MasterCard, Visa, American Express and Discover Card.
The RAC skycaps at Disney resorts know when fees need to be paid and when fees are not applicable. They have visibility to the airline systems, so they know when a passenger has elite status, or is flying in a class of service that does not require fees, or has used an airline credit card that provides free bags, or is immune from bag fees for some other reason.
To be on the safe side, call Baggage Airline Guest Services at 407-284-1231 to ask about bags between 50 and 70 pounds. Also call Disney's Magical Express Guest Services at 866-599-0951 to get the official, current Disney position. Then please return to this thread and post what they tell you.