Actually zoros fought 2 opponents before more than once and been fine defending himself, the issue with the gyhukimaru one is he thought gyuki wouldnt attack, poor judgement on his behalf. Even kawamatsu said they had werent really trying to kill each other when he saw them. And besides random items popping in and out would just be sliced through with ease.
1. Depends on the quality of his opponents, in this case he was facing Killer. Maybe it was Killer who was too strong to fight without other distractions? That would be the more logical conclusion to reach here.
2. Zoro already blocked Gyukimaru earlier in that chapter when he was distracted [click], Heck Gyukimaru even let Zoro know he will wait for an opportunity for when Zoro is distracted, so he was well aware Gyukimaru could and would attack, because well...quite frankly he already did, just moments before, so yea this excuse is not cutting it unfortunately.