Is the dMAT harder to prepare for than the GRE or TestAS?

The dMAT is not harder than the GRE or TestAS, but it is narrower. It has three fixed Core subtests with no broad syllabus at all, unlike the GRE's verbal-quant-essay format or TestAS's broader undergraduate-level content, which changes how you should prepare for it.

Why narrower changes your strategy

Because the format never changes between sittings, cramming is largely pointless for the dMAT, but timing discipline becomes essential. Your goal is speed and familiarity with the fixed task types, not covering a wide body of content.

Where the real difficulty comes from

Many Indian students from Engineering and Commerce backgrounds find the GRE's Verbal section more challenging than its Quant section. The dMAT's difficulty, by contrast, comes almost entirely from unfamiliar task types, particularly Latin Squares, rather than from advanced content.

As a result, a well-prepared Indian STEM or commerce graduate can often close the gap on dMAT format-familiarity faster than on GRE Verbal vocabulary.

My Advice

If you are also preparing for the GRE alongside the dMAT, sequence your effort by return on time invested. dMAT format-familiarity closes faster with focused practice than GRE Verbal vocabulary typically does, so do not let dMAT prep crowd out the longer runway your GRE Verbal score genuinely needs.