Parsons doesn't have the physique to handle 300 pounds fulltime for a season. Eventually it will wear him down and severely shorten his career. I could see him playing in a rotation but that would be wasting his talents.
Parsons is a rookie linebacker and he and the team has got to take some lumps while he acquires experience at the position. Consider it an investment into the future and that future could even pay off later this season. He's going to make some mistakes but I believe he will learn much quicker than the average rookie.
In the end, we will have a dominating linebacker capable of lining up anywhere and that will be far more productive than an EDGE playing one side of the field. For now, help is coming in a few weeks, we will get T-Law back.
With T-Law and Gregory at EDGE in addition to a Parsons getting batter each week at linebacker, it will form a very powerful triangle of speed that can defend the field on both sides as well as the middle, where the Cowboys had been struggling the most. Add in the recovering DT's along with Osa and the OLBers Neal and LVE and the Cowboys front seven will be solid.