I think your analysis will be proved correct. The Yankees had a real shot to win a championship this year, but Cashman blew it when he failed to upgrade the starting rotation. Maybe he would have acted if the Astros acquired Grienke 24 hours earlier, I don't know, but I do wonder if the timing of the Grienke trade (last minute) was part of the Astros strategy. As we all know, the Astros are an incredibly smart organization. Once the Astros acquired Grienke, and the Yankees were left with nothing, the contrast between the two organizations became very clear.
Sure, the Dodgers didn't do anything either, but the Dodgers were looking for bullpen pieces, not rotation help and the Dodgers believe that they have the young arms in the farm system who can help in the bullpen in October. I think they plan to move Maeda to the bullpen in October as well.
Want to have a good laugh? Project the Yankees starting rotation in October and then compare it to Verlander, Cole, and Grienke. Depending on who they play in the first round, the Yankees could be one and done in the playoffs. If the Yankees get lucky, maybe they make it to the ALCS, but the Astros will destroy them, similar to how the Red Sox totally destroyed the Yankees in the playoffs last year. There will be a lot of upset Yankees fans this October. Can't wait.