It would be better to replace the SSD, read write speeds and all that y'know. I'm not saying you shouldn't get a big ol sd card, I mean, dankpods got doom eternal running off an iPod's hard drive, but it's not something you'd wanna deal with every day
I'd say it depends on the types of games you probably play? Maybe?
Have the 64Gb one with a 256Gb SDcard, and been perfect for the games I play (hades, stardew valley, emudeck also quite good), I know it'd probably be faster with an SSD but not looking to invest the time or money to upgrade just yet. Really happy with it
The only game so far I've definitely noticed slow load times was star wars jedi fallen order, that was the most resource demanding game I've played on the deck. Sometimes took like 30secs to load the game or respawn, but after that the whole game was quite normal.