The command gets run on the server, and increases the max size available for
any template on the server, not on a site by site or list by list basis.
You said you are doing this in SPD. In that case are you sure you are
saving just the list and not the whole site as a template? You can do the
same thing from inside the list settings in the UI and then you'll be sure
you are getting just the list. Just go to the List Settings for the Task
list you want to save and use the Save List as template link. Then go to
the new site and create a new Task list based on the template you created.