This is the oft-repeated trope that keeps being come up with, but please look how actually correct it is.
Corbyn won because, in the two leadership elections he faced, he was the one most likely to win a general election out of all the candidates in those elections. Even if you expand the field to encompass the self-described "big beasts" in the Labour establishment, he would still probably have more chance of winning than any of them (which is why they did not stand, either the first or second time).
The idea that there is a viable alternative for Labour to turn to right now is daft; there is either taking a gamble on Corbyn (who for all his faults has at least boosted Party membership and engagement, and promoted debates on actual policy) or surrendering to the evident failures that are the Progress faction in the PLP (who, lets not forget, lost the last two elections, who lost Scotland, who would probably lose Wales next, who cut party membership in half, who built up huge debts and who ran the party into the state whereby Corbyn could win a leadership election in it).