Interesting comparison. Though I believe he was comparing GBA to Switch, not GBA to phones. Phones just exhibit a similar trend (older phones were smaller than current ones).
There’s always been a market for the large portable console, also with the promise of docking. It’s just that compute was difficult to achieve until recently, and the market for the small end has been eaten by phones, and so they only make the larger end now.
See https://en.wikipedia.org/wiki/List_of_handheld_game_consoles...
But realistically, there’s always been three categories to personal compute and gaming.
For lack of better words, mobile, portable and home use.
Mobile was the gameboy and now the mobile phone.
Portable back then was the game gear and sega nomad. Today it’s the switch, steamdeck, and for a while the PSP and PS Vita. These provide cut down versions of home console games or better fidelity than truly mobile.
Home use being permanently plugged in like the SNES/N64.
It’s not that the small handhelds have gotten bigger, it’s just that they’ve stopped making stuff in that smallest category.
The fact is that mobile phones have taken over that mobile market completely. There’s no space to compete so that market is dead for game console makers.
This has been the trajectory for decades now.
It seems in all categories people tend to purchase devices with larger screens. I wonder if this is caused by the nowadays much larger proportion of adults using these devices, where the Gameboy, etc., we're seen more as children's toys - meaning smaller form factors and screens might have been a better fit.
Those sorts of games are best suited to smaller screens but that’s the market that smartphones have basically taken over.
So if you need to differentiate a gaming product from the smartphones that everyone owns, you kind of need things like bigger screens, better ergonomics and more immersive games etc