the Solid ground and pound that you mentioned can be argued by his performances against Randy, Mir 1 and Mir 2
In addition, his submissions skills would not be needed as most heavyweights are not BJJ black belts.
Furthermore, He was able to take Cain down however, Cain is very elusive and a decorated wrestler where he has been able to get back to his feet quickly. This fight is dependent on Lesnars top control and if his wrestlign is 'that good'
Note: When Lesnar won the NCAA title, it was a weaker division than when Cain won.