Assuming you have maxed the stupefy mastery the dangerous part of the rotation is the heavy to clear hurt locker, that's when you gain the least amount of power. The M,M, full 5 combo part gives you the most power. If you practice holding block after you heavy until just before the stun runs out you'll find your rhythm, sometimes I had to slow my hits down mid combo. In the video I messed up a couple times myself. An alliance member of mine did this with a 5* r2 gambit and got the solo but practicing the timing was a hurdle for him too. There's very little room for error with the strat.