I'm perfectly happy with that position, as long as you are happy to extend the same logic to your own POV?
The assistant manager has been chosen by the manager clearly, rather than the DOF.
Why is optimistic until proven otherwise a better standpoint to take?
Edit: re coaches being out of date - im responding to the idea he's been hired for his prem knowledge. If you want prem knowledge hire someone who has coached in the modern prem surely, not someone who played for Fulham nearly a decade ago.
I am not taking an optimistic position by default though. I haven't even commented on it, until now. I'm taking a neutral position by default because we genuinely don't know anything about the appointment, good or bad.
Would I expect the manager to have more of a say in his own assistant than the DoF? Yes, I would. That makes absolute sense and if anything, it would be very weird to impose someone that the manager doesn't know/want on him.
I doubt he's been hired for 'Prem knowledge' personally, whatever that means (I know you didn't come up with that, you're just responding to it). It's not the 1950s. The Prem is very cosmopolitan, ideas and tactics are international, and there are very few secrets or league-specific factors that would warrant hiring someone with 'Prem knowledge'.
Speaking English and understanding the way English clubs generally operate is probably an advantage to some extent, but overall I'd assume the main criteria are the obvious ones (being tactically aligned with the coach, being a good communicator, being a good motivator, being a good judge of character/ability, improving players).