Whoever said that has never worked on an updated roster or offseason roster. For legends rosters it's not that big of a deal. For current rosters, it is a big deal. Overwriting someone that later signs with a team means that you deleted their audio which you can't get back. Then you need to edit someone else to replace the guy since you now have to edit the original player back who no longer has audio.
Also allowing only 131 create a players slots (currently) is going to hamper the efforts of offseason roster creators. There are 253 draft picks every year and another 100 or so Udfa's that make the roster not including practice squad players. So you have to figure out 250-300 players to overwrite to have an accurate offseason roster before the next Madden comes out.
Being that you can only do full edits to players in Franchise mode, you can't just edit whoever you want if you plan on sharing the file. You have to figure out who retired and match them up as best you can or use unsigned low rated players and hope they don't get signed.
3135 is too low of a number when the initial roster has 3004 players. I can't figure any reason for them to limit the game to this number except that they don't want people creating offseason rosters because they are afraid it will eat into sales numbers for the following year. From at least M12-M16 there were around 400 create a player slots, so this is definitely a step backwards the past 2 years.