Running with other people 7 days a week for a couple of years helped me improve substantially but then running by myself 5-6 days a week boosted me further. I was not a fan of marathon-pace runs. I did plenty of 8K/5mi tempo runs at faster than marathon pace but anything longer than that was slower than marathon pace. I raced often though, including many 12K cross country races each season.
Running with other people 7 days a week for a couple of years helped me improve substantially but then running by myself 5-6 days a week boosted me further. I was not a fan of marathon-pace runs. I did plenty of 8K/5mi tempo runs at faster than marathon pace but anything longer than that was slower than marathon pace. I raced often though, including many 12K cross country races each season.