As a Canadian, I'm envious. We have 11 daily flights between our two biggest cities, taking 1,5 hour. Or we have 6 daily trains that takes 5 to 6 hours. And freight has priority.
I know Germans like to whine about their trains being late, and AFAIK it's deteriorating, so they are right to expect better. However, they still have the option and that must help in reducing the number of internal flights.
It sure is complaining on a high level. But not complaining would mean to accept it.
It's also symptomatic for all the other deteriorating infrastructure and services (streets, bridges, power lines, non existing high speed internet, schools / equipment, public agencies, and so on and so on). All due to cost cutting, while at the same time taxes and prices increased. Those 16 years of Merkel (conservatives) ruined so much and left us completely unprepared for modern problems. And now the same geniuses blame the greens for not fixing it all in three and a half years.
Just swap the managers of the airlines with he Bahn, and soon there will be cheap connections all across Europe 4 times a day for 20 euros with competing train lines.
The problem is not the price or lack of service, but the trains being on time, so you do actually make connections. The only way to fix that is to improve infrastructure and that takes time.