There are 2 part in IDT. First is GST with weightage of 75 marks out of 100 marks. GST Bare Act pages are only 120 (please download CGST & IGST Bare Act from CBIC website & see total number of pages) V/s Income Tax Bare Act Pages are 1065. In addition to this, there are significant case laws in Income Tax. According to ICAI, no case laws in GST.
CA Final Student are smart enough to analyze factually.