“As Germany once you commit to a non-mobile force, your power projection plummets.”
This is spot on. You could go further, and say that most of the money Germany spends on anything other than Armor, Mechs, and Bombers should be limited.
Part of my position re: the bluff SL is that used to do the 1 CV/2 TT buy most games, deferring to the 2 SB/1 SUB concept, but not sure either one is the best. Anymore, I don’t add more than 1DD G1-3 to the surface fleet, I just leave it as it is, because even modest purchases (DD, CV) draw down your punch. If UK fleet is weak, and KJF, then I do buy some subs to annoy UK and potentially threaten SZ 91. And of course, a few infantry, as they will be needed to protect Rome, Norway, France etc.
Since Armor and Mechs are slower than bombers, and hitting Russia early is crucial; its probably more logical to buy armor/mechs early then bombers late (G4-6) because they can attack Moscow the turn after they are produced, assuming the invasion is going well.
All this concerns the critical path, as G40 is built, Germany spending money on ANYTHING other than Moscow punch is a recipe for a more stalemated game. To your point about shucking guys to Leningrad, its a 2-step move, and the former USSR factories themselves pumping out tanks is far better, so if I can grab the Ukraine and Leningrad factories as early as possible, that is better than putting 1$ on the water because pouring the tanks (ie money) directly into the fray is best.