This is a crazy formation. If the match simulation is good, the team adopting this formation will loss in this match. But the match simulation engine is not good enough. I understand it is not easy. So the illegal formation is meaningful! it at least punishes the team adopting such crazy formation. Even if illegal formation restriction is still in place, the team using it may not lose. Ball procession is not very important factor to match result. So in my opinion, the managers who like freedom to use formation can use some illegal formation if they want. They will just suffer slightly.
P.S. For those who don't know, formation with 1 defender is used to be a illegal formation. The ball procession will be changed to 80:20.