And the thing is, if you say the 7D has no reach advantage over a 5D2 then you must also agree that usage of TCs is always a waste....
First of all, the money shots
there can't be compared meaningfully because they are not the same FOV, and therefore do not target the same output result. For the purpose of advising the OP we are talking about the final output IQ of a 5D2 image that has been cropped to match the FOV of the 7D or t2i. One has to ignore the pixel count and pixel densities, because these numbers by themselves do not meaningfully predict the outcome of such as test.
secondly, I have to admit I'm struggling a bit to see the equivalence of using optical multpliers versus cropping the final image. The comparison is interesting, to be sure, and valuable in its own right, but is not nearly as simplistic as stated. To be sure, optical multiplication introduces side-effects of its own but these are heavily dependant on the TC itself and the native lens to which it is attached. Taking those into account, the advantage is that with careful choices one can present a larger image magnification to the sensor, decreasing the FOV opticallly while taking full advantage of the sensor's native resolution and IQ. This technique will advantage the FF body, and represents a very different test case than the OP has presented. For example, take a photo, properly exposed and framed of course, with the t2i and a 300 f/2.8 lens. Then add the 1.4 III to the lens and mount the combination on the 5D2 body and crop the resultant image to match the 1.6 crop factor of the t2i. is there any doubt as to which will produce a superior result in more situations? To take the experiment further -- mount a 2x III to the 300 f/2.8 and take a photo with the 5d2, then take the TC off and take the same photo with the t2i, croping the result to match the FOV. 5D2 wins.
All that aside, in conversations about "reach advantage" the optical vector to the discussion is irrelavent anyway because it misses the point. the point is that in distance constrained situations, where the limit of optical magnfication has already been reached (think "I'm gonna have to crop even the 7D image just a bit"), one cannot suddenly outfit the FF body with a different optical system to answer the question.