I loved her. Not my favorite but I enjoyed her style. Oumi's deal was that she was gonna give the opponents bazooka spikes for at least 2 sets anything after that, don't expect her to score as much which is where Koga came in perfectly unless they used Oumi as sub she was a total nightmare. She was kinda easy to target since she isn't persistent like you said also unlike sakoda her serve/back row isn't as explosive. Reception was meh. Still NEC was fun because of her.
She had excellent reception which was insane. Maybe not as good as Hayashi but she dealt with blows really well. The season she was set to retire she wasn't at her best shape anymore and I think the season before that she got injured so probably by then her reception was falling behind but I agree her pipe was not as devastating as Sakoda's.
She had a title at NEC some type of Japanese firework.... I forgot what it was. But again she was very short, shorter than Mayu so she never had much of a shot to make it to the A team plus it didn't seem like she cared about that stuff.
Hisae Watanabe was fun to watch but Oumi was the full entertainment. Energy level like Kobata and was very charismatic.