I agree with this. Oikawa is a team player, his atyle wouldn't have mixed well with Washijo's "individual strengths" mentality. The team wouldn't play all that differently imo, and I have two main reasons for believing that .

1) Ushijima has unintentionally mastered the art of pissing Oikawa off, and we've all seen how he acts when he loses his cool. It simply wouldn't have worked. He would have concentrated on drawing more out of the other players - like Leon or Tsutomu - while neglecting the ace simply out of spite.

2) As a left-handed left wing spiker, Ushijima can play at nearly 100% by default because he is just that hard to play against. So, even if Oikawa were to eventually make an effort to work together, he wouldn't be able to draw that much more out of him. It's like trying to imagine Fukuroudani playing with Kenma as a setter. The other players would do better, but the team's gameplay wouldn't improve much overall bc Kenma simply wouldn't be able to deal with Bokuto's mood swings like Akaashi can.

Long story short, the others might have a bit more playing time, but the setter/ace combo wouldn't work as it should. So either they would reach the same result with a more compact team and a poor setter/ace combo, or the whole dynamic would be compromised. They wouldn't have the outlet of the Ace to get them out of tough situations bc they simply wouldn't cooperate.