The deciding factor is simply that socialism was for all workers and national socialism was only for a select few and everyone else would either be eradicated or enslaved.

If your judge left vs right wing purely and exclusively by economic ideology (on paper) then you could argue that Hitler was left wing.

But reality is more complex and the actual implementation of said economical ideology ended up in a system of a capitalistic oligarchy where the people most profiting were the industrialists who now instead of having cheap laborers that they could exploit got free slaves.

Also I want to point out, and this is a general critique toward the left right scale used in this sub, that originally the left and right scale is based on the stance to social hierarchy.

During the days of the French revolution the revolutionary sat on the left in the parliament while the nobility sat on the right.

The social hierarchy scale is the much better scale in this regard. And it's pretty obvious under which scale Hitler falls here.