There are a lot of different opinions about feeding. It kind of depends on how much you believe they should have a balanced diet or even which type of balanced diet you think they should have. The layer feed has everything in it, vitamins, protein, calcium, that is needed for them to most efficiently produce eggs. If they eat nothing but the layer feed, they will do well and produce eggs. It does not have a lot of supplements beyond the minimum requirements, though, such as stuff to improve the appearance of the feathers. It is intended to produce eggs efficiently and not cost you too much compared with their competitors are charging so you will buy it.
With that said, there are some differences in layer feed. Whether those differences are worth your extra money is your decision. You'd have to study the list of ingredients and know what the different ingredients provide to really make an informed decision.
The layer feed does contain a lot of stuff they need. If they eat too much of something else, say scratch or cabbage, they may not eat enough of the layer feed to get their daily requirements of certain vitamins or minerals or maybe not enough protein. It can be a bit of a balancing act. A hen that produces an egg a day is making something that makes up a pretty good percentage of her body weight. She needs to eat well.
The most common recommendation I have seen is to only feed them enough treats so they can clean them up in 10 to 20 minutes. This supposedly does not cut into the minimum daily requirements they get from the layer feed enough to cause any shortages. And if you vary the treats some, they will probably get the extra things they can use that the layer does not provide.
This may sound complicated, but what I am recommending is to not give them too many treats and vary those treats somne, which it sounds like you are doing with various vegetables, hopely some of which are greens.
Your reasons for bringing in the feed are valid. Just make sure you are storing the feed overnight in a way that is not attracting mice inside.
Good luck!!!