It is clear what Spong would be able to accomplish in stand up exchanges. His resume speaks for itself and he would definitely get the better out of most LHWs and dare I say even HWs. Obviously the issue would be how would his lack of experience in wrestling and jiu jitsu fair against MMA fighters?
One thing I will say he does have working for him is being out of that terrific camp the Blackzillians. With guys like Rashad, MJ, Thiago Silva, Alvarez, and JZ... you got to think he can improve in the grappling department.
Look at Stephen Thompson for example. Had an easy fight for his first... then gets ambushed by Matt Brown... gets easier matchups after to slowly bring him back up, and now his takedown defense has improved and most recently was also able to knockout a ranked MMA fighter with wrestling credentials.
Why can't that same approach be done for Spong? That's of course if he has interest in MMA full time which I am not sure he does.