The standard buster sword is also an unwieldy weapon by definition and any blade that large would be extremely easy to read the attack patterns of, the sheer size doesn't allow for much variance in the strikes. Plus, as Captain America's shield does absorb kinetic energy, as was stated, he could easily break any kind of combination attack Cloud attempts to make to the point in which he'd throw Cloud's balance off entirely. At that point, the Captain would tank Cloud in no time at all.

Also note the intelligence boost. Cloud's unstable at best, and Captain America should have no trouble outsmarting him. Combat isn't just about speed and strength, if you are a smart fighter you can come out on top more often than not.