breakdown of teams offseason improvement or not

I try hard to follow teams in the offseason to see if they make improvements or if they lose key players. But the offseason is long, there are great backups waiting in the wings that only local fans sometimes know about, and often players like offensive linemen will slip threw the crack in terms of media attention. i've found websites that grade free agents and say where they end up, but does anyone know of any free websites out there that grade teams on whether things like the running attack, passing attack, offensive line, and defensive will improve or probably get worse from last year? it would be a major help in ranking players/teams in terms of projected fantasy output. i'm not interested in solely rankings in fantasy terms because those are very easy to find and often some of the "experts" are a little too opinionated and subjective about where players will end up. or are just following the hot trends. i think this would prove a more objective ranking and let me make some of my own calls. Thanks.