By the time PQ3 was produced, a great amount of people worked on each of Sierra’s games. That is obvious. However, Jim Walls has (and still is) always been perceived as the brain behind Police Quest – the invidual from which spawned the chief creative drive behind that franchise. That didn’t happen by accident, which is why I find it impossible to attach much weight to your statements.
Anyway, I don’t believe we will ever know the truth behind Walls’s split from Sierra. A few months ago I was related an explanation that with some thinking makes a whole lot of sense. (For fear of offending anyone, I don’t intend on repeating it. Don’t ask.)
And regarding the PQ1 remake – it was a sad, unnecessary remake (i.e. ripoff) of a glorious game. As with the SQ1 and LSL1 remakes it failed to make any money. And to further strengthen Jim Walls’s position, we may also point out the quite unplayable (i.e. not much fun) Open Season. It clearly lacked the sparkling wit of the Walls Police Quests.