I’m not sure how that gets accounted in different schemes, perhaps it is somehow impossible in ERC grants, but it is certainly the case in some grants.
25% cap would I think make most universities bankrupt overnight.
Sorry, this is just not true
as PhD ("Doktorand") Student/Finisher, you will get around 45.000 EUR - 60.000 EUR in most jobs, maybe there are some mega corps like BMW or Siemens which will pay more (or consulting or IB etc.), but the vast majority of jobs with a "research background" in Germany will NEVER land you near 100.000 or more
1.800.000 / 50.000 (avg) is 36 persons, somewhere in the ballpark range i mentioned
In Europe a PhD student is a multiyear commitment, with a bunch of externalities, they are much simpler to manage as discrete units, and thus are funded as such.