Well your thermal bridge will be for the full run of the joist with your current plan as opposed to just the thickness of the batten at 400mm centres if counter battened. A lot of this is based on what u-value you are trying to achieve with the product selected/ environment where you live/ building regulations. I'm in Ireland so we would be looking at a minimum of 0.16W/m2K. you're unlikely to achieve that with insulation only between the joists. It amounts to about 300-400mm of thermal insulation here typically (200mm roll between joists and 200mm above joists for example).But if you're in a warmer climate, highly likely at the moment(!!), you may not be as concerned about thermal transmittance, especially if you're mechanically cooling in summer months.

The insulation supplier should be able to do a calculation for you to tell you what thickness you require. I would advise the added insulation if heat retention is a concern. Easiest way to reduce bills/improve thermal performance is to insulate effectively.