Its a Mechanic. You work around it.
Random boss resets are *also* a mechanic (albeit unintended), but that doesn't mean that they're not stupid/broken/etc. Whether the developers' intent was to have an attack that had a more averaged damage dealt (law of large numbers means that 5 attacks are more likely to behave in a normal manner than 1 attack) or to specifically have an attack that specifically disadvantages Shad/Sins (Shad/Sins have substantially lower mitigation outside of KW/DW; any mechanic that bypasses or diminishes the uptime or effect of it, is specifically disadvantageous towards Shad/Sins compared to the other tanks because of that reliance), we would need to get a developer response. No matter how you put it, it's a mechanic that specifically makes it harder to be one variety of tank over another (and I'm not entirely sure I see a reason why Shad/Sins should be disadvantaged since there is the heuristic balance between tanks insofar as KW is balanced against the higher passive DR of VG/PTs and Guard/Juggs and the CDs are considered to be relatively consistently balanced).