Obviously Ryan isn't playing at a super high level. For example, he's not doing any blocks or counters.You can't deny that there are some pretty terrible design decisions. Forcing instant fail challenges to finish the game. Penalizing characters for not speccing one way or another*. Dodging doesn't extend the combo counter. There's no timer or fade on the combo numbers to let you know how much time you have. Enemies don't spawn in at a more constant rate.
Also challenges like this are never great. Darksiders had them at the start (although they never got as tough as the 9th ring in Inferno). It feels contrived and forces you to use skills that aren't always needed for the rest of the game. It's fine to add an extra challenge for extras like in Batman or God of War 1/2, but if those skills are necessary they should be rolled in more smoothly. GoW did a decent job by making enemies that are susceptible to juggling, or placing you in rooms that are closing in on you.
No game ever requires you to combo an entire group. It's a goal to try and achieve, and if it gives you bonus experience or something that's fine positive reinforcement. It should never be required to finish a game.
*The idea of being underleveled for a boss doesn't apply here, because you can't go back and relevel more.