If you imagined the pulley was exactly the same size as the wheel, then pick whatever wheel size, and the torque is the same.
In your example btw, a 90T HTD 5M pulley would have a circumference of ~450mm => diameter of 143mm, or around 5.6 inches. Not bad for a 9 inch wheel or whatever.
I do see the appeal of this drive though: achieving higher torque than you could ever get with like a 14T motor pulley and idlers, or whatever is the realistic minimum we use.
However I don’t think adding another belt and pulley is worth it just to use a higher kv motor. (Extra inefficiencies from more moving parts) Would love to be proved wrong though.