Reading gurobi reference manual I found this:
We have also found that certain classes of MIP models benefit from reducing the thread count, often all the way down to one thread. Starting multiple threads introduces contention for machine resources. For classes of models where the first solution found by the MIP solver is almost always optimal, and that solution isn't found at the root, it is often better to allow a single thread to explore the search tree uncontended.
Another situation where reducing the thread count can be helpful is when memory is tight. Each thread can consume a significant amount of memory.
In the past, when I used a shared server, users were requested by IT to manually limit our thread limit to 1. Now I am working on a dedicated server with 8 threads available.
As we can see from gurobi's manual, one could choose which thread limit benefits your goals (for worse or better), so that the maximum number might not be the case for better/faster results.
For an academic research and publishing, what is the fair practice when comparing comercial solver results with non parallelized heuristics?