No! Please do not cut back on feed, ESPECIALLY when working with Leghorns and EEs, two high production breeds.
Free ranging supplements a commercial mix. It should not in any way replace it. They should have 24/7, 365 day per year access to a commercial mix AND be allowed to free range. The best free ranger in the WORLD couldn't obtain more than 20% of their diet from free ranging, and the majority will not acquire even that. Even if they could, it would be detrimental to them - I'll explain why in just a moment.
The most common thing I hear in response to this is "But my grandmother/grandfather/long lost great uncle did this when they were kids! All of their birds did just fine living off the land and foraging from the scrap piles and compost bins!" And yes, 50, 80, 100 years ago, chickens did generally survive off what was available, and maybe supplemented with some seeds or grains by their keepers. But those were the breeds of 50, 80, 100 years ago. The advent of commercial rations perfectly suited to a chicken's nutritional needs was a turning point for almost every chicken breed out there. It has allowed their bodies to be pushed to the limit of what they can produce - in the course of 50 years, we've doubled peak egg production from 150 eggs (a world class layer back then) to 300 being the AVERAGE for a production breed. The domestic chicken is derived from Junglefowl - a group of species which, on average, produce maybe 5-15 eggs per year.
Almost all breeds you encounter being sold at hatcheries can be expected to produce 200-300 eggs per year on average. Your Leghorns are some of the peak producing fowl, where less than 300 would be a poor layer. Hatcheries like to call breeds they carry such as Leghorns or Plymouth Rocks "heritage" because a breed of that name has existed for a couple centuries. But the actual genetics of the stock sold by such hatcheries is recent - very recent. Unless it comes from an Old Standardbred line, it's a patchwork creation made in the past 50 years or so and is without a doubt what I would call a modern breed.
Think of a modern chicken's body like a delicate and powerful machine (because it is). It performs at the peak of its capabilities, and it takes very careful upkeep to keep it performing well. The more eggs a hen produces, the more her body has been tinkered with to obtain a better producer, the more delicate the process of keeping her in good condition. And feed is without a doubt the number one factor in keeping a bird healthy.
Yes, free ranging is good for them. Actually better for them than most any scraps people love to feed their birds, since they're obtaining a perfect mixture of proteins (bugs) and vitamins/fiber (plants) without consuming anything overly fatty, sugary, or otherwise imbalanced and without over-consuming anything either. But it should act only as a supplemental ration and nothing more.
Regarding scratch - even if there was some way to cut back on feed during the spring and summer months without negatively impacting their health and production, feeding scratch as a replacement would be a really bad idea. Scratch may look like something nutritious, but it's basically chicken candy - I can't think of a substance worse for a chicken's health than scratch. It's fatty and contains little to no actual nutrtional value. And almost everyone overfeeds it; I can't even count the amount of birds I've had brought to me and after handling them have found them incredibly obese; and upon asking their owners, "Do you feed scratch?" their response has almost always been, "Oh, yes, I feed X amount per day to my flock of X hens!" (X amount of scratch and hens usually being something ridiculous like 1 cup to 6 hens - I wouldn't suggest giving more than a 1/4 cup to that amount of birds and probably not even that!)
And lastly: if you do want something that can survive largely off the land, you'll need to sacrifice egg production. The only breed I know of being capable of obtaining more than 20% of its diet from free ranging is the American Pit Game. These types of birds are the most commonly found breed of stray chicken, because sometimes they wander a little to far or get chased away from their homes. Not that modern breeds don't do this too - the difference is that these guys actually stay alive long enough to be found. They have gone feral in places such as Hawaii, Florida, and even here in sunny California - in a busy urban area no less. This is because Pit Games are cockfighting fowl; for the last 10,000 years the only selection which has gone into them has been to increase their aggression towards other fowl, which is a hormonal characteristic, not a physical one. Meaning that their biology, aside from their gamy tendencies, has remained close to unchanged in the past 10,000 years of domestication. They are still very much a wild thing, just one which has calmed down enough to live peaceably with humans. But that's the kicker - they cannot be expected to produce well in any way. I have one; she gives me a decent number of eggs, perhaps 50-80 total, in the spring and summer; and her production ceases entirely during the winter and fall. She is considered a very good layer for a gamehen; most will produce fewer than 50.
