Dogen's answer to hongaku's central difficulty has a name in his own writing, shusho ittou, practice and realization as a single, undivided thing. If awakening is not a future state produced by practice but the ground practice already stands on, Dogen concluded that sitting meditation cannot be a technique aimed at a later result without misdescribing what it actually is; zazen is not preparation for buddhahood, it is buddhahood being enacted in the present sitting, which is why his Shobogenzo treats the question of why practice matters if awakening is already given as resolved by rejecting the premise that practice and its goal are two separate things at all.
Shinran's answer comes from the opposite direction and reaches an opposite practical conclusion. Where Dogen trusted disciplined self effort to express an already present awakening, Shinran concluded that nothing in a deluded practitioner's own effort, however sincere, could be relied on to accomplish or express anything, and that the entrusting mind itself, the very capacity to have faith in Amida's vow, is not something the practitioner generates but something given from outside. Both readings start from the same original enlightenment premise Tendai handed the Kamakura reformers, and both arrive at teachings, formless sitting and other power reliance, that scholarship treats as genuinely opposed rather than as variations on a shared theme.