I don't see how you can argue otherwise, it just burns (or in the case of a short bbl, spews out the muzzle) too much powder for what you get in return.
The simple formula I use for calculating cartridge efficiency when comparing those of different caliber is to use ft/lbs generated divided by powder grains used. I try to make it a more even playing field by using bullets at about the same point in the weight range for a given cartridge.
For instance, .243 Win, I'd use a 100 gr. bullet and average the powder charge required for max velocity. To compare that to the .25-06, I'd use 115 or 117 gr. bullets and average that load data. To throw in the .270, I'd use 140 grain bullets. I use the same barrel length whenever possible.
So, take your .243/100 gr. combo. In a 24" tube, it'll top out at ~3,100 FPS for ~2,100 FPE, and requires an average charge of ~43 grs. to do so. That's roughly 49 ft/lbs per grain.
Now take the .25-06 and a 117 gr. bullet in a 24" tube. This load also goes 3,100 FPS, generates 2,550 ft/lbs and and requires an average charge of ~52 grains. That's also ~49 ft/lbs per grain.
Now the .270/140 gr. An average charge of ~56 grs. will get you 3,000 FPS for 2,800 Ft/lbs. That's ~50 ft/lbs per grain.
Of course there's some latitude in the numbers that depend on a lot of things, but this does serve to demonstrate that the .25-06 is
not really that inefficient. Fact is, any of the higher velocity cartridges in a given caliber will be less efficient than their smaller, slower counterparts. That's just the nature of the beast.