Schedule isn’t the root cause. DB has serious problems with staffing, because their workforce is going to retire soon in large numbers and finding replacement is hard. They have problems with infrastructure: it is telling that a heavy rain, moderate snowfall or burning grass can knock out a major route. Both are management problems.

Trains being late isn't that overrated. Its not the most important thing, but it is important. Because being late messes up the whole system. One train being late can cascade to lots of other trains being late. Causing system degridation.

There is not one single issue with the German network. Yes, the multi polarity you mentioned is one of them. But that's not the main issue, really more a feature.

One of the issues is that early on DB wanted to continue to make money with cargo, so they insisted on having cargo (and other trains) use the same lines. Rather then building new lines that nobody else uses. This choice over long term degraded to a situation where lots of high speed lines are just major upgrades of existing lines.

That leads to the network not having as much capacity as it could have had. And you have ICE trains blocking lots of the tracks for other trains, and the other way around. And even if the ICE can go, it can't go full speed because some parts aren't upgrade enough. You constantly go from a speed line, to an upgraded line, to a normal line, to a city approach.

While its great that in Germany the ICE goes to the main station, unlike in France where Paris doesn't even have a real main station. It also leads to ICE trains having to use an excessive amount of the old city network. And there are always issues there. Just last week our train was lolligaging around the approaches to Hamburg.

There is also just a general maintenance issue, personal and so on.

That all said, having traveled threw Germany a lot with the train just in the last couple months, overall, I think its amazing. But could be so much better still.