The difference from normal to OLED Switch was bigger because of the jump from 6.2 to 7 inches. Far more noticeable and a big thing if you prefer handheld mode. Steam Deck has “just” a jump from 7 to 7.4 inches (good enough for me).
Yes the OLED screen is better and there are minor upgrades overall, but the LCD modell is still good an if you dont care you can now get a used LCD Deck very cheap because everyone is selling theirs now. I just saw 1tb Decks for around 350-400€ and thats criminal cheap compared to the 569€ and 679€ that valve is asking for the OLED models.
Just keep in mind the Power of the OLED models is basically the same.
Thief: The Dark Project Replaying retro games in handheld mode is so much fun to me.