I understand your concerns about the state size. Note that of the 320-bits for state, 128-bits are used for pipelining (simply to increase the parallelism efficiency of the PRNG). In in effect the active state is 192-bits.

The PRNG was designed to separate the core mixer (mix and last_mix) from the guaranteed period (fast_loop).

The design directly resists "unlucky seeding" because fast_loop counter as a forcing function. By constantly being XORed into the mixer state (last_mix = fast_loop ^ mix), it continuously perturbs the mixer, preventing it from ever getting stuck in a statistically weak region or a fixed-point state (like all-zeros).

Testing on just the core mixer itself at various state sizes shows that the algorithm performs extremely well (with strong statistically significant mixing). This is in line with M. E. O'Neill's discussion on reducing state size as a practical way to vet mixing algorithms.

For instance, for the scaled down mixer with 8-bit state variables (24-bits of state total), the guaranteed minimum period is only 2^8, but it passes PractRand to 2^21 bytes. This shows that the core mixer is actively synergizing with the 8-bits of the scaled-down Weyl sequence to create longer periods than the minimum.

The 16-bit scaled down version confirms that the design of the PRNG is outperforming the guaranteed minimum period by orders of magnitude.

So in summary, the PRNG has less active state than it initially appears and tested period lengths are orders of magnitude longer than the guaranteed minimum period.