Parables are analogies, but never perfect ones. [The Parable of the Burning House] provides an image of four separate vehicles. But if we follow the teaching of the sutra as a whole, the One Buddha Way is not an alternative to other ways; it includes them. A limitation of this parable is that it suggests that the diverse ways (the lesser carts) can be replaced by the One Way (the special cart). But the overall teaching of the sutra makes it plain that there are many paths within the Great Path, which integrates them, i.e., they are together because they are within the One Way. To understand the lesser ways as somehow being replaced by the One Way would entail rejecting the whole idea of the bodhisattva-way, which the sutra clearly does not do. In fact, the whole latter part of the sutra is a kind of extolling of the bodhisattva-way. Also, in the story itself, in running out of the burning house the children are pursuing the śrāvaka, pratyekabuddha, and bodhisattva ways. In terms of their ability to save, the three ways are essentially equal. They all work.
A Buddhist Kaleidoscope; Gene Reeves, The Lotus Sutra as Radically World-affirming, Page 191