William,
Your assertion that the 336 cannot handle the 307 is correct, and validated by Marlin itself canceling the 307 debut after only a few prototypes were built.
The reason Marlin released the 308 ME is to copy the 307 with a cartridge friendly to the 336 action. The 94 big bore action was designed for the use of 50,000 psi cartridges. The 336 is at its best with cartridges that generate less than 45,000psi. Were both the 375 and the 356 shoehorned into the 336? Sure, but this does not mean the marriage is ideal.
Marlin itself has admitted that pushing the 50,000psi level results in sticky extraction, and is the upper limit of the design strength of this action.
By the way, Marlin has, in a sense merely reinvented the wheel with both their 308 and 338 cartridges. This is not to disparage either, but the fact remains for handloaders, both cartridges will have real performance levels below both the 307 and the 33WCF.
I suppose Remington has sealed Marlin's fate. Since FN destroyed Winchester, its all falling like a row of dominoes. Suspect that we will see a drop in Marlin quality, similar to Winchester, as the workers already know the noose is closing, and loose all interest in the company they helped to make.
