I for one *sincerely* doubt the very deep Theban column had anything to do with "push weight" - it would appear to me as physically impossible for even a fraction of the depth to contribute their "weight" to the match, nevermind now without flatly crushing the front-rank guys.

Overly focusing on the hoplite column also entirely misses the importance of the contribution the Theban cavalry made by variously distrupting the Spartan ranks and harrying their flanks and rear.

Rather, it would appear to me that the point of the exercise was to leave rather major chunk of the Theban hoplites in the flank of the Spartan line after the immediate resistance was routed - and in excellent position to roll up the whole thing from the side. After all, consider the tactical situation this left the remaining Spartans in - not only were they facing fresh and unengaged, if rather thin, hoplite line to their front, but also had a veritable army (including the the Sacred Band, the Thebans' hardcore shock troops) right in their side and busily wheeling around towards them...
"So tell me... do you feel lucky, punk ?"