I don't think McLellan had much to do with it.
Eberle just didn't work with McDavid, so he was moved away from him at 5v5 and on the PP pretty quickly.
He and RNH disappeared without Hall carrying the offense on that line. Neither of them could get the puck through the neutral zone if their life depended on it.
That's not what I saw... what I saw was:
1) Two years ago Pouliot - RNH - Eberle was our best line. And RNH was the driver
2) Enter McDavid and RNH (and others, but especially RNH) are asked to start taking on vet-like, defensive focused roles... the message is finally sinking in
3) Ebs gets his extended audition with McD and after initial synergy in 2016, this year he and McD can't mesh... mostly Ebs is snake-bit at first, then it affects his confidence and the wheels fall off
4) Meanwhile, Drai is driving a line on his own and RNH has been pushed further into a defensive checking role... now instead of carrying the blue line, penetrating the first D and then passing off, he has "matured" to the point that he gains the line, jams the breaks (every time) and only makes a penetrating pass about 20% of the time,,, the rest of the time it is button-hook and pass back to the D or into the corner to start the cycle.
My point: I think this was all a matter of team dynamics, guys adjusting to new roles, listening to coaching and overcompensating a bit.... plus in Eberle's case, an intense desire to mesh with a generational player which led to complete loss of confidence.
NYI is going to love a "fresh start" Eberle... and we lost this trade.