Nature would not devise individual solution but would design the simplest process. All the above difficulties may indicate a natural and simplest planet formation mechanism.
Thus, we propose a model in which there exists an inner hole of the disk without specifying its physical origin.
Dusts naturally 1)fall toward the outer edge of the hole, 2) rapidly coagulate in this dense coherent flow to form huge proto planets, 3) which slingshot a proto planet inner/outer, 4) gas accretes onto the outer shot planet.
cf) dead-zone arguments https://arxiv.org/pdf/1811.09756.pdf

Planets are common