wow 600 Q, did you have all +3 mats? i notices that after you pass the 200 or so Quality things get a little bit harder, even with food. yes there is a randomness to crafting but you can somewhat turn the odds to your advantage. Check the hours element and use a synth with the proper crystal for that hour, also know what your stats do, Control does not help you about element stability, control helps you avoid sparks. and last know when to stop, yeah you might be able to hit 600, but if you see that @ 450 things are getting harder an harder, switch from careful/standard to standard/buffed rapid (for me rapid is risky so i tend to buff to make sure it hits the spot ^-^ ).

if all this fail dont worry, soon you will HQ with more easy since items made with HQ items will be HQ 100% after 1.19