I'm not sure that the World Tour system has had that much of an impact. The big teams are stronger relative to weak ones than they used to be, but that's mostly down to quasi-national teams and a few very rich individual enthusiasts making more money available to a few teams than can be extracted from most potential commercial sponsors. That wouldn't really be effected by a changed race qualification system.
If anything, getting rid of automatic race admission for teams 13 through 18 might make things substantially worse. Smaller WT teams, mostly ones with commercial sponsors, are already offering their sponsors lower expectations of success because of the market distortion created by sponsors willing to pay more than a commercial rate. The one thing they do have to offer is a guaranteed participation at the big races, primarily meaning the Tour. Without that, those smaller WT teams would have trouble justifying even their smaller budgets to sponsors.