When we say "trainable" we mean that the prospective pilot of a heavy jet will be capable of getting "up to speed" after the typical 20 hours of initial Sim training, ...and within 50 hours of supervised line flying. In frequent instances we have found that pilots without previous jet experience need more time in training, primarily because they're "behind" the faster airplane. This is just a statement of fact, not patronization.
At large airlines like UA, DL or AA applicants may be taken by the hand and given whatever additional training is necessary to get on the line. But my airline is not in the training business as such.