Believe it or not, the 25 rule benefits the players. First, think about this. In a five year cycle, you can sign 125 players (assuming redshirts), but the roster can only be 85, so you can have 40 kids leave the program, or 8 per year (33% attrition) and still be at 85.
If teams were allowed to sign as many players as they wanted, you would see kids pushed out of programs on a large scale, especially when there is a coaching change. The rule forces coaches to try to keep and develop some kids that they could probably replace with either new recruits or transfers. Ole Miss signed 38 kids in 2009 (although not all made it to campus), but that meant kids on the roster had to be pushed off scholarship.
What the transfer portal has done is make the transfer process more transparent as previously transfers were negotiated through back channels. The problem with the portal is kids are denouncing their current scholarship without a landing spot. Kids think that since they were heavily recruited as high school athletes that they will be highly sought after as transfers and it has never worked that way as there are reasons why kids transfer.
One last point on the portal. Most of the kids in the football portal are walk ons looking for a school to offer a scholarship which makes sense.