Yep that does happen and ultimately the goal of all this is that some sort of concensus is reached.
The benefit is that you get a few seats representing curb setbacks and a few seats representing cancer kids and they both have to work together to make anything happen. As opposed to USA where voting for curb setbacks means the cancer kids get no seats.
I think an important feature is that (as far as I understand) politicians in EU vote based on their issue whereas politicians in USA vote based on their party regardless of issue. And in Europe there's lots of referendums for when the politicians can't agree on something. The big stuff is often decided via direct instead of representative democracy.
So in your example of cancer kids, the party would probably make a big ruckus, then run a few polls to force a referendum, then a few months later everyone would directly have to vote yes/no on the issue. Obviously the parties would run voter campaigns to convince you to vote the way they'd like, but at least they don't get to just decide these things based on whom 50.5% of the country voted for a few years ago.
It's also, I think, a lot easier in [most of?] Europe to refresh the government. I can't even remember the last time a parliament in my home country managed to last a full 4 years without someone forcing an election. The UK in 2022 famously had a prime minister that lasted just 44 days.
We change our politicians like underwear. They're there to do a job not to build empires.