As many have acknowledged from the beginning of the discussion, there is not a lot of practical difference in the field performance of the 308 and the 30/06. that is NOT the same as saying they are equivalent.
Using your logic; Why would I want a 308. when a 7-08 do the same thing?.
Then one could argue that a 260 will do the same as a 7-08, and so on.
Where do you draw the line?
My favorite whitetail cartridge is a handloaded 257 Roberts. I think it's a sweet spot when one considers trajectory, recoil, and effectiveness. I've killed deer with everything from a 223 to a 300 Mag. If the right bullet is used, i can't say i have seen a big difference in the results.
BUT that is NOT the same as saying the cartridges are all equivalent.
One last time: the 06 case has more capacity that the 308 case. Loaded to the same pressures, the 06 has the ability to push the same bullet at a higher velocity. Ergo, they are NOT equivalent. Now, whether the difference is significant, is a personal judgement.