In my mind there were two versions of the Oilers last year:
1) Good version - forwards were getting back deep defensively and supporting the breakout as a unit. Heavy back pressure to stifle other team's breakouts and strong goaltending.
2) Bad version - forwards are blowing the zone as soon as the defense gets possession and completed passes become few and far between through the neutral zone. Point coverage and coverage in front of the net awful. Goaltending might bail them out (as happened a few times prior to the COIVD shutdown), or they get caved, but either way it isn't pretty.
The fundamental flaw with this team last year was consistency breaking the puck out efficiently. The common theme in both versions of the team above was shaky breakout passing and getting through the neutral zone with possession. To me the Oilers' success basically came down to how committed the forwards were to getting down low and helping the D move the puck out.
The good months (October, November, January, February) saw the Oilers forwards do the right thing in all ends of the ice. In the bad months (December, start of March, playoffs) the forward's commitment on their own half of the ice was terrible and they paid for it.
The solution long term is to have more d men that can actually make a consistent strong breakout pass, which should be coming (Barrie, Bouchard, Broberg, more ice for Bear and Jones). In the mean time the forwards have to commit every game to getting back and being competent in their own end. Nurse, Larsson, Russell and to a lesser extent even Klefbom are some mix of incapable of hitting a breakout pass or extremely inconsistent in doing so. Put a mobile, fast moving defense like Colorado has with our group of forwards and we would be unstoppable.