I am not bad at rapid (1100)
I am not bad at daily (1000)
I am not bad at bullet (1000)
but I suck at blitz (800) , why ? why is blitz different from other time ranges for me ? and how can I improve ?
Rapid ratings are inflated compared to blitz ratings. You are not worse at blitz than at rapid. Here is a site where there is a lot of data for comparing blitz and rapid ratings https://www.chessratingcomparison.com/Graphs
Ñ