Hoplitai too weak ?

[Geticus]

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 ?"

Xenophon was a contemporary of Leuctra and I think he outranks all other historians to write on this matter, due to his superior military experience as strategos of the 10,000 in Asia etc., and his text is clear that othismos of the 50 shield deep Theban mass broke the Spartan phalanx.

Xen. Hellenica 6.4.12-15

[12] Such, then, was the cavalry on either side. Coming now to the infantry, it was said that the Lacedaemonians led each half-company three files abreast, and that this resulted in the phalanx being not more than twelve men deep. The Thebans, however, were massed not less than fifty shields deep, calculating that if they conquered that part of the army which was around the king, all the rest of it would be easy to overcome. [13]

Now when Cleombrotus began to lead his army against the enemy, in the first place, before the troops under him so much as perceived that he was advancing, the horsemen had already joined battle and those of the Lacedaemonians had speedily been worsted; then in their flight they had fallen foul of their own hoplites, and, besides, the companies of the Thebans were now charging upon them. Nevertheless, the fact that Cleombrotus and his men were at first victorious in the battle may be known from this clear indication: they would not have been able to take him up and carry him off still living, had not those who were fighting in front of him been holding the advantage at that time. [14] But when Deinon, the polemarch, Sphodrias, one of the king's tent-companions, and Cleonymus,7 the son of Sphodrias, had been killed, then the royal bodyguard, the so-called aides of the polemarch, and the others fell back under the pressure of the Theban mass, while those who were on the left wing of the Lacedaemonians, when they saw that the right wing was being pushed back, gave way. Yet despite the fact that many had fallen and that they were defeated, after they had crossed the trench which chanced to be in front of their camp they grounded their arms at the spot from which they had set forth. The camp, to be sure, was not on ground which was altogether level, but rather on the slope of a hill. After the disaster some of the Lacedaemonians, thinking it unendurable, said that they ought to prevent the enemy from setting up their trophy and to try to recover the bodies of the dead, not by means of a truce, but by fighting. [15] The polemarchs, however, seeing that of the whole number of the Lacedaemonians almost a thousand had been killed; seeing, further, that among the Spartiatae themselves, of whom there were some seven hundred there, about four hundred had fallen; and perceiving that the allies were one and all without heart for fighting, while some of them were not even displeased at what had taken place, gathered together the most important personages and deliberated about what they should do. And as all thought it best to recover the bodies of the dead by a truce, they finally sent a herald to ask for a truce. After this, then, the Thebans set up a trophy and gave back the bodies under a truce.

The critical passage 6.4.14 in Greek reads:

14] ἐπεὶ μέντοι ἀπέθανε Δείνων τε ὁ πολέμαρχος καὶ Σφοδρίας τῶν περὶ δαμοσίαν καὶ Κλεώνυμος ὁ υἱὸς αὐτοῦ, καὶ οἱ †μὲν ἵπποι καὶ οἱ συμφορεῖς τοῦ πολεμάρχου καλούμενοι οἵ τε ἄλλοι ὑπὸ τοῦ ὄχλου ὠθούμενοι ἀνεχώρουν, οἱ δὲ τοῦ εὐωνύμου ὄντες τῶν Λακεδαιμονίων ὡς ἑώρων τὸ δεξιὸν ὠθούμενον, ἐνέκλιναν

The Greek is more explicit as to othismos because it uses the present participle of the verb Otheo in both instances to describe the action. The above translation is not my own, but taken straight from the Perseus website, a more literal translation of the first emboldened passage would be:

upo tou oxlou othoumenoi anexoroun
being pushed by the throng [the Spartans] fell back

and the second passage

os eoron to dexion othoumenon, eneklinan
as they saw the [Spartan] right being pushed back, they [the Lakedaimonian allied left] gave way

Sorry I don't type in Greek, but this passage is perfectly clear, the oxlos [throng] of the Thebans pushed back and broke the Spartan right, causing a chainroute down the whole Lakedaimonian line. I trust that you will concede that when Xenophon refers to the Theban oxlos (throng) he is referring to the previously mentioned 50 man deep mass cited in 6.4.12, and not some partial 12 man phalanx that you propose, which would never have dared to presume that they could have alone routed the hitherto invincible Spartiate phalanx led personally by a Spartan King. It took a military genius (Epaminondas), revolutionary strategy (oblique attack to the left) and unprecedented mass (50 shields deep).