Nintendo held back portable gaming technology.

I disagree.  The various competitors over the year have tended to fall into two groups.  One has more powerful hardware, or things like lit color screens back when Game Boy didn't.  However, those all suffered from problems like high price, bulk, or eating batteries alive.  Those would be the Game Gears and the Lynxes, and to a lesser extent the PSP.  The other group had similar hardware at a similar price; that would be the Neo Geo Pockets and the WonderSwans.

If Nintendo were behind so much, shouldn't another company have been able to produce something clearly beyond at a similar price?

However, in GBASP Nintendo included things like a rechargeable battery and the first lit screen that didn't suck power.  If Nintendo was holding things back so much, why didn't someone else make moves like these much earlier?