The problem with hybrid teams are that there tends to be in-person communication happening in the in-office teams which the remote employees aren't brought up to speed on. That creates alienation and preferential treatment. And the latter is important since it isn't a blinded scientific experiment and the manager gets to pick and choose how to interact with the two different teams, which is going to shift the outcomes. If the manager was remote-only with 8 remote employees they'd have to adapt to 100% remote work and the bias would likely evaporate.