I believe years ago rosters were around 100 or so and top programs brought in more talent than they really had room for , just for competitive advantage.
Many of players on the roster were just meat in a meat-market with out hope to get on the field and with the transfer rules in place made them sit a year if they wanted to find a program they had a chance of getting playing time.
Dropping down a level was the best choice and I believe some programs encouraged that so they could open up a roster spots for more talented players that would be bench material so they couldn't help other programs that might be on the schedule.
The move down to 85 was to stop hording the talent some programs were doing and it helped the game.
Now even with the transfer rules making it easy to transfer without penalty , the move to 105 rosters will just hurt the type of talent that wants to play but the school plans to hoard so rival programs have to wait until those players realize the program they're at really has no use for them and never did .
That's the way I see a 105 player roster , even in this era of transferring at the drop of a hat