I took a trip from the Netherlands to Romania, and amazingly only had a single transfer.
At least, that was the plan, but then a train went missing on the way there and we had an additional transfer. Pretty stressful. Way home was super smooth though.
The one thing I don't get the EU doesn't bring down the hammer on is getting directions and buying tickets. Feels like that should be a relatively easy fix, forcing all European rail companies to align from the top down. But I'm probably unaware of something that makes that harder than it seems.
Pretty much all train companies are vast old overcomolicated state-run monoliths that are very used to everyone working around them in their own country. Such organisations suddenly having to work together with others as equals requires a culture shift. Not to mention the technical challenges, the IT systems - if they even have any, or any from this century - are typically vastly different. They'd have to invest massively in modernisation and standardisation before they can even think of integration. This requires a multi-year effort and a lot of investment, which many states are not ready to make.
Sauce: the Swiss state-run train company SBB/CFF/FFS is and has been working hard to integrate the systems of just our neighbours, and it has been .... interesting.
Oh yes, I'm not doubting it would be a multi-year effort, it's more that I'm not aware of any such effort being in progress. Like, couldn't the EU at least have set a goal of interoperability in x years?