IDK, maybe I would feel different if I used laptop on the go more, but I doubt it. Having a mobile phone seems to cover it now.
I think you raise a good point though. I'm automatically suspicious of free WiFi.
Some do (especially those in markets with relatively cheap plans or large data allowances), others don't.
You have access to a nice plan - and that's good - but not all EU countries have nice plans and cheap prices. Someone in, say, Portugal doesn't have a local "100GB for €20" offer. They probably also can't get the same offer you can because your provider will ask them for a local address, a local bank account, there will be a different language, etc.
Most providers also have rules on how long you can use roaming for, so it's unlikely that you can just pick a plan from a French provider and use it in Germany (or multiple countries) for a year straight... For that you'll need a travelling eSIM or something like that, but is anyone offering a travelling eSIM with 100GB for €20 a month?
Essentially your mistake is assuming that everyone in Europe can get 100GB for €20. Some can, some can't. And that's the problem.
For one thing, that bypasses the German requirements regarding presenting a physical id in person to get cell service.
It’s possible that only works well for travelers though.