We have had this discussion before. lol There are certainly some limitations, but nothing which cannot be overcome. The equipment is decent enough, no major issues. Since they left the 70s style helmet, all is good there. That was my only concern in terms of equipment.
Yes there will be filler teams, but there were 26 teams in the NFL in the 1975.
As I mentioned before, you can get past many of the issues by not using Franchise mode, but instead using Play Now and keeping track of everything yourself. That allows you to modify and use custom playbooks which mimic the playcalling and style of the '70s.
This roster is not for everyone, I understand that. It will not be as popular as some of my other rosters, but it is a bit of a personal challenge and something I want to do.
This year, in Franchise, you can edit the weights and heights and faces, so those can be fixed by the user once the roster is downloaded. Now, I might, no promises, make those edits in my own Franchise file and then, if possible, save that file and post it somewhere so people can download it outside of the game. I do not know how simple that process would be, but it is potentially an option.