> In your opinion, is it more likely to work with this software
> for that kind of fillet task ?

No, not really - filleting is not a particularly strong area of Rhino either.

I tried Rhino on this case and it's slightly better in that it doesn't make as much of a mess as MoI (in MoI v2 the filleter will return partial results if it was not able to calculate the full result, unlike MoI v1 where it will just do nothing) but just leaves an open hole in that juncture area.

ViaCAD is much better to use for more difficult filleting than either MoI or Rhino, it's actually very inexpensive ($99).

- Michael