unfortunately i don't think you can dissociate the business aspect of the fashion industry with the design direction, especially in this day and age...
Hmm...you do realize that having left a big brand, not just once, but *twice*, does place Heidi Slimane in the same category as those you mentioned, NG, Jil Sander, MM, etc.?
I think this opinion, that somehow design brilliance is blighted by unsuccessful tenure at big corporations, is somewhat fringe - most of us here, who still post threads about the design careers of MM, Helmut Lang, NG, Jil Sander (when she was in the wilderness), didn't let their quarrels with their respective CEOs affect our esteem for their status as fashion legends. Business, art and creativity mostly exist in separate universe, many great artists never sold their works profitably in their lifetime and the reverse is also true - commercially successful designers and brands do not always command the same awe and respect, some of the biggest fashions businesses out there come to mind, from high-street to high-end.
In the end, critics' opinions matter little when the concepts, ideas and looks catch on like a virus. However, other than staunch (verbal) support from bloggers and twitters, I haven't noticed the looks by Slimane coveted and copied by the fashion crowd and in the streets, even after it was worn by Lady Gaga, the ultimate uber-celebrity.
I'm super practical, I don't have personal biases about designers, I am only bothered by badly designed collections.
Here's hoping that Slimane shuts his critics up with his next collection!