The ADATS should be 11.3 BR, its missiles are not worth 11.7 either as ground or as air. It’s not an effective fighting vehicle for ground anyway making its ability to defend itself niche and irrelevant.
Probably that’s why Gaijin couldn’t find any meaningful statistics on the 2S38.
Gaijin likely separates data of intentionally up-BR’d vehicles.
Thus only using 10.0 data.