The Vega56 is faster over 85% of the time running below 4K. It also comes with 2GB more RAM than the typical 6GB config of a 1060.
There is only about 12 months difference between manufacturing dates, but typically, newer tech is better when it comes to hardware performance and when taking depreciation / longevity into consideration.
If they cannot fulfill your RMA, I would buy something better, (maybe even a refurb) and sell the replacement when it comes. This gets you back in the "game' and offsets the purchase of your new card. Not ideal, but worth considering.