My Steam Deck is a second wave pre-order 256GB modern, and that is exactly my feeling. Between the internal 256GB and the excellent Steam Deck micro SD utilization, it was good enough that I never opened it up just to change the SSD. When I started to get some stick drift, I finally upgraded the SSD at the same time.

The 256GB is “good enough”, but 512GB is “enough” and 64GB is tight.