If you feed with plain pH'd water, it will start to die again. Plants in DWC need to be in nutrient water for their whole lives or they will suffer from deficiency and ultimately death. The idea of giving seedlings watered down nutrients is like giving a baby watered down milk out of fear of burning its mouth with "full strength". Its not drinking gallons of milk, only what it needs!
If normal strength nutrients causes seedling death, why don't they die when planted in supersoil? In soil, you start with enriched soil and end up with depleted soil on harvest. Why do people think it's the opposite in hydro? Plants always want a good concentration of nutrients, not just adults. The quicker you start them off with a good concentration, the quicker they take off.
The reason noobs are generally told to underfeed is because in the past, they had a tendency to overfeed... but now it seems like there's more of a tendency to underfeed. Plants want "just right", not "less is more" or "more is more". Less is not more unless you're overfeeding, which you're not.