Maybe, it's too early to tell for sure. You certainly correct it can work for a year or two.
You're allowed a total of 85 full scholarships but you can only give out so many a year - I forget how many. The system is built to favor using the majority of your scholarships on players who will be there for the full four/five years. In the past, a lot of coaches in trouble would push hard for lots of JUCO transfers who only had two year of eligibility. They could build great teams, but in the third year, they started to run into having less than the full 85 players on scholarship which kills depth. I suspect in a few years, teams that put too much emphasis on Portal transfers are going to find they their dozen or so stars but only 70 to 75 other players on scholarship.
We've seen first hand what happens when you aren't over 80 players on scholarship.