I am trying the mechanical mesher where it is possible to put only elements representing the boundary layer without necessarily adding inflation, do you think it is better?

But it's hard to get good quality. As you said earlier, my mistake can be caused by the mesh, it can be that the skewness is too low, but even using both mesh, the good quality is still hard to get. Should I refine more and more knowing that I am already at :
For a station that has only 4 cores and 15GB of usable ram?