If you have 12 or 14 equally sharp managers you can play with just about any rules and you'll have a good keeper league. The problem is most leagues don't have that owner equality & before too long 1 or 2 teams will have 10 top 100 players and a couple will have 2 or 3. Having something in place to help the teams with bad rosters or bad luck being able to bounce back in a year or 2 is very important. Unless you like replacing owners every year & trying to find owners to join your league & face impossible odds.Having 10 or 15 keepers is great for the owners of the best teams, or having Heyward for the next 5 or 10 years at a discounted salary is great for that manager. The good owners with good teams will keep coming back, but you need to look out for the weaker or unlucky owners when setting up the league.
When asking for roster advice in these pages, remember there are thousands of different sets of league rules & many different active roster settings. If you want the best replies, be sure to include your leagues particulars in the original post