It solves it, as much as adding a trailer to your sports car solves your problem of not having a pickup truck. It works, but it's very inconvenient.

Eventually those boards run into limitations and then you have to just opt to go with serial to a microcontroller which misses the entire point of having a SBC.

I agree that its not the ideal solution. Still would be better to use a SBC like the Raspberry Pi or other boards. But was just pointing out that if GPIO needed to interface with slower hardware like relay boards or sensors , then there is an option.