So when I pot clones or pop seeds (just did some seeds yesterday).
I saturate my medium with 2L to 3L of full strength veg nutes (GHE tripart), that is in a 20L fabric pot. Never had any issues with stunted growth and the medium stays moist for around a week as it mostly evaporates over time as they don't drink much.
Even if the medium is still a bit wet after a week, I will give a bit of feed as well but not the full 3L per pot. My grow environment is likely different to yours though - RH, temp, air flow etc.
I always feed with nutes though, you have your 2nd set of true leaves there as well. Never tried to get seedlings going in coco without nutes, but never had issues either. Not saying it is needed as I know seedlings can go without nutes for upto 3 weeks, just easier for me and I make sure to PH obviously. It does not do any harm. The nutes are then available for when the seedling is ready.
Auto's can be iffy at times though, the most issues I have experienced have been with auto's. Pop multiple seeds at once, some have amazing growth and out of say 5 one is just super slow. Never had this with photoperiods and I have popped a lot more photo seeds.
I really doubt it is your light. You could lower it a little if you really wanted to but I don't feel that is necessary.