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The partial combined arms patch notes rebalance tank armor/guns/resistances to a new system/paradigm. Tanks all lose their armor values, but their guns/other AV all do reduced damage to compensate. The skyguard was not included in the current round of changes and so its damage is abnormally high at this time.
I read this and went to double check. Against an MBT, the Skyguard time to kill is equal to or longer on PTS than it is on live. Same with a baseline Sunderer and a Harasser. Against a Lightning in a few cases the TTK does get shorter but it doesn't immediately appear to be a significant amount.