I agree with basically everything you did. My point is that they want people to join to have a higher degree of organisation within the industry.
Also, in the German system, it is considered highly unusual to have two different types of contracts for union members and non-union members. If any employer tries to do that - and of course they do - the unions are usually going to war. And rightly so. “Wahrung des Betriebsfriedens” is a goal for both employees and employers, but one job - one pay (etc) is a political goal the unions fought for long and hard.
Again, you are absolutely right there is a strong neo-liberalist tendency to undermine that. And if the degree of organisation falls further, the IG Metall will have a serious problem. Hence the publicity-making call for 28 h: get people discussing, involved, and organised. That’s the pitch, and that’s the project, from my POV.