IMHO, the Oilers' offense is built primarily and predominantly to "feed McDrai". Lines not having one of McDrai seem to be little more than time-killers to give those two a breather -- if they score, great, but its not really expected. Thus, it shouldn't be a particular surprise that these downline players are not productive because the system is essentially designed for them to fail.
The "feed McDrai" strategy is a good one in the abstract with two such phenomenal players, but that also relies on them both being healthy and productive. If they get worn down or simply go cold, then the entire system breaks down. This is the precise opposite of a depth-scoring team.
Jackson's summer moves simply reflect this system: Load up on mediocre time-killers. Everybody and their dog saw that what the Oilers needed was upgrades on defense and a prime-time goalie, but under the Oilers system these things are low priorities (and last summer doesn't seem to have been a priority at all even with the loss of Ceci).
Also, it seems that time has proven through multiple coaches that it really doesn't matter who the Oilers coach is, because McDrai are simply going to do whatever they want whenever they want to do it. If they want to play together, they'll end up playing together even if they start out running separate lines.
Even with all these defects in their build, the Oilers can still be an extremely tough playoff team if McDrai are healthy and get hot. Otherwise, not.
My take anyway, please feel free to disagree. Viva la difference!